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Physics sinch chem was so long
Terms in this set (121)
T = F R sinθ
A wooden plank in the shape of a rectangle with side lengths a and b lies on a frictionless surface. Two forces, each of magnitude F, are applied to opposite corners as shown. What is the magnitude and direction of the net torque applied to the plank about its center?
A. aF / 2 counterclockwise
B. bF / 2 counterclockwise
C. aF clockwise
D. bF clockwise
D. From the picture, it is clear that each force provides a clockwise force about its center. This eliminates choices A and B. For two dimensional bodies like the rectangular plank, the preferred formula for torque is the moment arm equation, τ = lF, where l, the moment arm (or lever arm), is the component of r that is perpendicular to the force. Another way of thinking about the moment arm is that it is the distance from the pivot to the line containing the force. In this case, l = b / 2 for both forces. Since each torque is in the same direction, the net torque is twice the torque provided by either force.
Moment arm (lever arm) def and equation
the perpendicular distance from the line of action of a force to a specified axis of rotation
A 10 kg, 4 m long plank of wood is going to be used as a teeter-totter for a brother and sister. The brother has a mass of 30 kg and the sister a mass of 20 kg. If the brother and sister sit at opposite ends of the plank, how far from the brother should the fulcrum be in order for the teeter-totter to be balanced?
To solve this problem, we use the equation for the center of mass in one dimension, remembering to include a term for the mass of the plank,M, at its geometric center (i.e. the midpoint of the plank). Setting the location of the brother as the origin (x1 = 0), we see that:
centripetal force equation
A bobsled team of four men, each of mass m, pushes the sled of mass M over a horizontal displacement d before leaping into the sled and beginning to slide down the hill. The total length of the winding track from the top of the hill to the bottom is L, and the height difference between the top of the hill and the bottom is Δh. If the sled starts at rest and we assume the whole track is frictionless, how does the final kinetic energy of the sled at the bottom of the hill (prior to the brakes being applied) compare to the initial potential energy of the sled at the top of the hill?
A. KE f > PEi
B. KE f = PEi
C. KE f < PEi
D. It is not possible to uniquely determine the relationship between these two energies.
A. With no friction, this is a case of conservation of mechanical energy after work is done on the combined mass by the running men. The conservation relation can be written KEfinal = PEinitial + Wexternal or, if you take the speed achieved by the bobsled team just as they leap into the sled, KEfinal = PEinitial + KEinitial. Either way it is clear that the final kinetic energy exceeds the initial potential energy of the sled.
Kinematic Equation derivative and pair
when finding MA what can we use instead of the forces?
we can use the distance travelled
Because the work involved is the same whether the mass is lifted straight up or pushed up the ramp, mechanical advantage can also be calculated as the ratio of the distance over which the force is exerted using the simple machine to the vertical displacement
Is it possible to have constant velocity and non-zero acceleration?
It's possible to have a constant speed and non-zero acceleration: try driving in a circle. Your speed remains the same but you're constantly accelerating toward the center of the circle.
But it's not possible to have a constant velocity and a non-zero acceleration, because velocity is directed speed: it's not just how fast you're going, but which way. In the previous example of driving in a circle, the acceleration is constantly changing the direction of your velocity; so your velocity is constantly changing even if your speed isn't.
-stationary or constant nonzero velocity
-constant speed and direction
Work output/work input x 100%
mgh(from machine)/Fd(by person)
A block with a mass of 5 kg starts at rest at the higher end of a 5 meter long tilted ramp. The difference in height between the high and low ends of the ramp is 3 meters. The ramp itself is smooth enough that friction can be ignored as the block slides down, but once the block reaches the ground, it experiences a kinetic frictional force as it slides to a stop. If the block slides to a stop in 6 meters on the horizontal ground, what is µk between the block and the ground?
C. Kinetic friction does the nonconservative work to bring the sliding block to a stop after its initial gravitational potential energy has been transformed into kinetic energy. Starting from the total energy conservation equation, the value of the coefficient of kinetic friction can be found from the work expression. Note that friction works over the horizontal ground, so the normal force is just mg, and that the block begins and ends at rest, so ΔKE = 0:
An ideal projectile launched from the ground at an angle of 45° up from the horizontal has a total flight time of T. Which of the following correctly expresses a relationship between the displacement d, velocity v, and acceleration a at T / 2 compared to time T (the instant before it hits the ground)?
A. 2 × |dT/2| > |dT|
B. |vT/2| = |vT|
C. |aT/2| > |aT|
D. v T/2 = 0
A. At half the total flight time, a projectile launched upward from even ground upon which it will eventually land will be at the apex of its flight. At this time, all of its velocity is in the horizontal direction (meaning it has slowed down, eliminating choice B, but is still moving, eliminating choice D). Its acceleration throughout the flight is a constant g downward, eliminating choice C. That only leaves answer choice A, which is correct: The magnitude of the displacement from the launch point to the apex is a diagonal line that is the hypotenuse of a right triangle with the max height of the projectile as one leg and half the range (R = |dT|) as the other. Twice this hypotenuse must therefore be greater than the total range dT.
seems to be equivalent to one newton*meter but is not considered the same since joules measures scalar quantities like work and energy
A lever is used to lift a 10 kg mass to a height of 2 m. If the person on the other side of the lever exerted a force of 50 N over a vertical distance of 5 m to accomplish this lift, what is the efficiency of the lever system?
B. Efficiency is the percentage of work output by a machine relative to the work input or energy consumed. In this case, the lever lifted a 10 kg mass to a height of 2 m, for a work output of mgh = 200 J. Since the person input W = Fd = (50 N)(5 m) = 250 J, the efficiency is 200 / 250 = 0.8 = 80%.
A soccer ball is kicked at a speed of 30 m/s at an angle of 30° up from the horizontal. How far will it travel horizontally before landing again on the field?
A. 45 m
B. 60 m
C. 79 m Correct Answer (Blank)
D. 150 m
C. To answer horizontal range questions, start by determining the time of flight. For that, focus on the vertical component of motion, picking a location where there is enough information to solve for the time. This occurs at the apex: .
pic for diag 1 q 18
Given the time of flight, the range is a matter of distance = rate × time, where the rate is the horizontal, cosine component of velocity and total time is twice tapex: R = 30 m/s (cos30°) × 3 s ≈ 90 m (.85) ≈ 77 m, closest to choice C.
A dimensionless number that indicates the factor by which capacitance is increased when a dielectric is placed between its plates.
A dielectric is an insulating material placed between the two plates of a capacitor, allowing for the storing of more charge (if the circuit is on) or a decrease in the voltage difference (if the circuit is off).
the value of charge, q must be:
a whole number multiple of the elementary charge 1.6 *10^-19C
A car is being lifted by a hydraulically powered jack. The area attached to the car is 100 cm2, while the area where the force is being input is 20 cm2. How much force must be applied to lift a 20 kN car?
A. 2 kN
B. 4 kN
C. 50 kN
D. 100 kN
A hydraulic lift operates via Pascal's Law. Hence the proportion of the force over the area is equal for both sides of the jack. In other words F2 = A2 / A1 ×F1, or solving for the applied force F1 = A1 / A2 × F2. Plugging in the numbers yields 20 cm2 / 100 cm2 × 20 kN = (1/5) × 20 kN = 4 kN.
no heat exchange (Q=0)
ΔU = -W
A process in which no heat is transferred to or from the system by its surroundings.
Heat is added to gas in a piston-cylinder, causing the piston to rise. Which of the following terms describes this process?A. IsobaricB. IsochoricC. IsothermalD. Adiabatic
A. IsobaricBecause volume is changing, this process cannot be isochoric (eliminating choice B). Heat is crossing into the system, so it cannot be adiabatic either (eliminating choice D). As heat is added, the temperature of the gas will increase (eliminating choice C), causing the gas particles to move faster. These particles push with more force on the piston, causing it to rise, expanding the volume, and thereby maintaining the pressure of the gas inside equal to the pressure on the piston. This makes the process isobaric since the pressure remains constant over the course of the process.
what does it depend on?
-the difference b/w the absolute pressure inside and the atmospheric pressure outside
Pgauge = P+Patm = (P0 + ρgz) +Patm
-When P0 = Patm, Pgauge = ρgz
depends only on denisty of liquid and depth of object
current has what unit?
ampere which is charge(C) per second
Coloumbs is charge
a measure of the resisting power of a specified material to the flow of an electric current.
Apparent weight of submerged object
weight out of water - buoyant force
Coloumb's Law and relation to electric field
Refers to attractive force between any two charged particles
realtionship between electric force, field, potential
The work done on an object equals the change in kinetic energy of the object
why does electric potential decrease mathermatically as a negative charge gets closer to positive
- Since the change in potential energy is ΔPE = qV and both ΔPE and q are negative, then V must be positive. This means the potential at point B must be greater than the potential at point A,
Total Pressure Equation
A test charge 2 nC and mass 10-8 kg is released from rest at point A which has an electric potential of -100 V and travels to point B which has an electric potential of -500 V. What is the speed of the test charge when it reaches point B?
The change in potential energy can be calculated using ΔPE = qV = (2 × 10-9)(-500 - -100) = -8 × 10-7. Since this represents a loss in potential energy, there must be a gain in kinetic energy of the same amount. Both the initial speed and kinetic energy are zero since the charge started at rest, so the entire change in kinetic energy is due to the new speed. Therefore KE = (1/2) mv2 and v2 = 2KE / m = 2(8 × 10-7) / 10-8 = 160 and v = √160 ≈ 13 m/s. Note that the exact square root is not needed since only choice A is close.
A dipole consists of two charges separated by a distance of 2 m. The charge on the left is 2 nC and the charge on the right is -2 nC. What is the value and direction of the electric field at a point halfway between the two charges?
A. 0 N/C
B. 18 N/C to the right
C. 18 N/C to the left
D. 36 N/C to the right
D. The strength of the electric field E from a source charge Q at any distance r from the source charge is E = k|Q| / r2 where k is Coulomb's constant. The principle of superposition states that the electric fields of multiple source charges can be added. The electric field from the left source charge is ELeft Q = (9 × 109)(2 × 10-9) / 12, = 18 N/C. The direction of ELeft Q is away from the positive charge and toward the negative charge (the direction of force a positive test charge would feel), which is to the right. The electric field from the right source charge is ERight Q = (9 × 109)(2 × 10-9) / 12, = 18 N/C. The direction of ERight Q is away from the positive charge and toward the negative charge (the direction of force a positive test charge would feel), which is still to the right. The total electric field is then 36 N/C to the right.
Saline is flowing at a constant rate through a syringe with a starting diameter of 2 mm and an ending diameter of 4 μm. How many times faster is the saline moving at the end of the syringe than at the start?
A dipole consists of two charges separated by a distance d. The charge on the left is +Q and the charge on the right is -Q. What is the value of the electric potential at a point 1/3 d from +Q and 2/3 d from -Q? Use k for Coulomb's constant.
A. (3/2) kQ / d
B. 3 kQ / d
C. (9/2) kQ / d
D. 9 kQ / d
A. The electric potential φ from a source charge Q at any distance r from the source charge is φ = kQ / r where k is Coulomb's constant. The principle of superposition states that the electric potentials of multiple source charges can be added. The electric potential from the left source charge is φLeft Q = kQ / (d/3) = 3 kQ / d. The electric potential from the right source charge is φRight Q = -kQ / (2d/3) = -(3/2) kQ / d. The total electric potential is the sum of these two potentials, and since potential is a scalar, there is no direction to be considered, so 3 kQ / d + -(3/2) kQ / d = (3/2) kQ / d. Note that completing the algebra is not necessary because once it is known that the coefficient must be less than 3, choice A is the only possible answer.
wrt electrolytic cells, the sum of reduction potentials should equal..
the voltmeter reading aka total cell voltage
REMEMBER: you do not need to multiply the reduction potentials if you multiply the equation. we only do this with enthalpy
For potentials, you reverse the signs if you reverse the equation, but you never multiply it by the coefficients, it is a intensive property, independent of stoichiometric coefficients.
all ionic compounds and all strong acids and bases since they dissociate completely in water
how concentration cell work
same electrodes seperaated in two diff solutions with same compound but diff [M]. the oxidation will occur to the electrode that is in the lower concentration solution.
there is no ,movement of ions between solutions
standard cell potential (E°cell) of concentration cell
will always be zero since reciprocal redoc reactions are occuring
the difference between the mass of an atom and the sum of the masses of its protons, neutrons, and electrons
when nuclei have too many neutrons relative to protons, it emits a beta particle. it increases the number of protons and decreases the number of nuetrons
easiest way to figure out the amount of radioisotope remains after a specific number of half lives
(1/2)^n tells us how much has gone
n: half lives that have elapsed
then subtract from whole to figure out how much remains
when do we use E=mc2
when mass is converted to energy
When measuring the mass of all particles involved in the fusion of two nuclei, 2X10^-31kg of mass is unnacounted for. Approximately how much energy must have been released?
alpha decay, beta decay do what?
a: loss of two protons
b: gain of one proton from one neutron. no change in mass number
Ecell= E°cell - (.06/n) (logQ)
I = Power/Area
refers to the emission of electrons from a metal when light shines on the metal
ke and pe of spring
Heisenberg uncertainty principle
it is impossible to know exactly both the velocity and the position of a particle at the same time
whay happens when mass on spring is doubled?
what happens when mass on pendulum is doubled?
the period is doubled
period is unchanged
currents going through resistors
voltage from batter is..
currents going in must equal current coming out
...equal to sum of voltage drops across resistors
sound wave through water
light wave through water
Sound waves travel faster in denser substances because neighboring particles will more easily bump into one another.
When light travels from air into water, it slows down, causing it to change direction slightly. This change of direction is called refraction. When light enters a more dense substance (higher refractive index), it 'bends' more towards the normal line
centripetal force relation with magnetic force
acceleration in spring mass system
If you consider a mass on a spring, when the displacement is zero the acceleration is also zero, because the spring applies no force. When the displacement is maximum, the acceleration is maximum, because the spring applies maximum force; the force applied by the spring is in the opposite direction as the displacement.
A person stands at an equal distance between two speakers which produce identical sound waves. If the person moves so that she is 1.5 m closer to one speaker than the other, she is in a "quiet zone" (i.e. the waves experience destructive interference). The wavelength of the sound waves could be all of the following EXCEPT: (A)0.6 m (B)1 m (C)3 m (D)6 m
If the path difference from two wave sources to the detector is an integer multiple of wavelengths, then the waves will experience constructive interference (i.e. compressions will line up with compressions, rarefactions will line up with rarefactions). This can be expressed as d2 - d1 =mλ, where d2 and d1 are lengths of the paths traveled by the waves, m is an integer and λ is the wavelength. Similarly, if the path difference is equal to an integer-and-a-half times the wavelength, the waves will experience destructive interference: d2 -d1 = (m + 1/2)λ. Since the waves are experiencing destructive interference, 1.5 = (m + 1/2)λ. So 1.5 could equal λ / 2 or 3λ / 2 or 5λ / 2, etc. Solving forλ, we get that λ = 2(1.5) = 3 or (2/3)(1.5) = 1 or (2/5)(1.5) = 0.6, etc. (all answers in meters). Choice D is the only answer not possible.
harmonic # in open pipe is equal to
number of antinodes
closed: odd number harmonics only
number of antinodes+nodes
A high current power line is supported 10 m above ground and carries a current from West to East. A negatively charged balloon is released directly below the power line and begins to float straight up toward it. What is the direction of the magnetic force on the balloon due to the magnetic field surrounding the power line?
Period of a Spring
ohms law and power
A high current power line is supported 10 m above ground and carries a current from West to East. A negatively charged balloon is released directly below the power line and begins to float straight up toward it. What is the direction of the magnetic force on the balloon due to the magnetic field surrounding the power line?
C. Find the direction of the magnetic field created by the wire using the right hand rule. The magnetic field under the wire points North. Once the magnetic field direction is found, find the direction of the magnetic force on the balloon using the left hand rule (since the balloon is negatively charged). The direction of the force on the balloon is to the East.
were looking for the force on the balloon. have to do RHR on balloon
from the convex mirrorwith radius 48 does an object have to be placed to form an image whose magnification is 1/3?
A. 36 cm
B. 48 cm
C. 96 cm
D. A convex mirror cannot produce an image with this magnification
B. A convex mirror has a negative focal length given by f = − r / 2, where r is the radius of curvature. f is therefore −24 cm. The magnification is given by m = − i / o where i is the distance from the image to the mirror and o is the distance from the object to the mirror. Since the magnification is 1/3, 1/3 = − i / o, so i = − o / 3. Plugging this into the mirror equation (1 / o + 1 / i = 1 / f) yields 1 / o + 1 / (− o / 3) = 1 / (−24). Simplifying, − 2 / o = 1 / (−24) or o = 48 cm.
Speed of a wave is only affected by ...?
When do frequency and wavelength change?
change in medium.
frequency and wavlength may change wrt same medium
BUT frequency never changes when changing mediums. if velocity increase in new medium, wavlength must change but frequency does not
average power(instantaneous power)
Average power for an AC circuit is IrmsVrms
where Irms = Imax / √2 and Vrms = Vmax / √2
what is frequency?
number of waves per second (s-1)
pipe waves and harmonics
How many times more intense is a 60 dB sound than a 20 dB sound?
D. The relationship between sound level (β, measured in decibels) and intensity (I) is given by , where Io = 10-12 W/m2. Instead of plugging each of the given values of β into the equation, solving for their respective intensities and then taking the ratio, remember an easy way of comparing sound levels: every increase of 10 dB corresponds to multiplying the intensity by a factor of 10. Since 60 dB - 20 dB = 40 dB, there are four "increases of 10" between them. According to the rule, this corresponds to multiplying the intensity by 10 four times (i.e. 10 × 10 × 10 × 10 = 10,000). So a 60 dB sound is 10,000 more intense than a 20 dB sound.
index of refraction equation
n = c / v
c: speed of light in a vacuum
v: speed of light in the medium
One light source emits bright red light while another source emits dim blue light. According to the photon theory of light:
A. each red photon must have more energy than each blue photon.
B. the red photons must be traveling slower than the blue photons.
C. the red photons must be experiencing less diffraction than the blue photons.
D. there must be more red photons being emitted per second than blue photons.
D. Whether light is thought of as a wave or as photons, all frequencies travel at 3 × 108 m/s in a vacuum and close to that speed in air. This eliminates choice B. (Note that even if the dispersion of light were considered, red light would travel faster than blue light). The energy of a photon is given by E = hf, where h is Planck's constant and f is the frequency of the light. Since the frequency of blue light is greater than that of red, the energy of blue photons is greater than the energy of red photons. This eliminates choice A. There is nothing in the question relating to diffraction, so we can eliminate choice C. (Note that even if diffraction were taken into account, red light diffracts more than blue light when passing through a small opening). The answer is D. Brightness corresponds to intensity, which is total energy per time per area. For red light to have higher intensity than blue light, there must be more red photons being emitted per second.
A guitar string is playing notes that are flat (frequency too low). How can the string be made to play the correct notes?
A. Increase the tension in the string to increase the wave speed
B. Increase the tension in the string to decrease the wavelength
C. Decrease the tension in the string to increase the wave speed
D. Decrease the tension in the string to decrease the wavelength
A. Intuitively, it makes sense that increasing the tension would cause the string to play higher notes, eliminating choices C and D. Specifically, increasing the tension increases the speed of waves traveling along the string:
v=radT/(m/L) where T is tension and m / L is the linear mass density of the string. Since the length of the string allowed to vibrate is the same, all harmonic wavelengths will be the same (since λn = 2L / n). This eliminates choice B.
Wave speed equation
frequency x wavelength
Wavelength of string is only dependent on
what does removing resistor do to current?
current in each resistor stays the same but total current changes
Energy equation of photons...
if power is constant...
E=Pt cause powe is energy over time
A block is oscillating horizontally on an ideal spring. If the amplitude is doubled, what would happen to the maximum speed of the block?
A. It would stay the same.
B. It would increase by a factor of .
C. It would increase by a factor of 2.
D. It would increase by a factor of 4.
C. To find the maximum speed of a mass on a spring, we use the principle of Conservation of Mechanical Energy with kinetic energy equal to (1/2)mv2 and elastic potential energy equal to (1/2)kx2. Comparing the energy at x = 0 (where the speed is at its maximum) to the energy at x = A (the amplitude, where speed is zero), we get (1/2)mvmax2 = (1/2)kA2 (based on conservation of energy). Solving for vmax, we see that vmax = which is directly proportional to A. This can also be recognized by examining the equation and creating a proportionality out of the non-constant terms: vmax2A2. Therefore, doubling A would also double vmax
kinetic energy of photoelectron
delta: work function of metal aka measure of binding energy
fluids in motion at same elevation
pssg 19 Q1
increasing speed, decreases pressure
pssg 21 very good examples for proportions/algebra for buoyancy problems 2, 3, 4
an object floating up from bottom of ocean will have what acceleration?
b. decreasing due to viscosity
c. increases from initial value due to increasing KE
d. decreases from initial value due to decreasing PE
drag force is pulling down
pistons and hydrolic lifts are described by which law?
the work done by either is the same but a mechanical advantage is provided in which the force needed on one will be less than the force applied by the other. this is becasue the distance on the first one is greater
Derived from Bernoulli's equation:
P1 + ρgh1 + (1/2)ρv1^2 = P2 + ρgh2 + (1/2)ρv2^2
ρgh1 = (1/2)ρv2^2
2gh = v2^2
EQUATION: √2g(h2-h1) = v
k value in coloumbs law
Capacitors in Parrallel
capacitors ins eries
in parallel: add like resistors in series
in series: add like resisitors in parallel
potential energies wrt charges
W=qΔφ=qV is used on moving a charge across an already existing potential difference
W=PEcap=1/2QV is used to represent the work the battery does to move the total charge from one plate to another
passage 31 good capacitance review
pssg 34 Q5
electric field produced by point charge vs...
E=V/d for constant field between parallel plates
r: internal resistance
V: terminal resistance
currents and voltages across parallel and series circuits
voltage drops across series. in parallel the voltage drop across EACH resisitor will be the voltage of the battery
current is split across parallel circuits. sum of all currents through the parallel resistors equals total current
longest wavelength harmonics
fixed string: fundamental frequency lambda=2L
constructive and destructive interfereence changes frequency how?
does not change frequency if initial waves were identical
Period of a pendulum
from one end to the other is half a period
important fact about frequency in simple harmonic motion
frequency is not dependent on amplitude
speed of light in a vacuum and within new medium
3.00 x 10^8 m/s
speed always constant within the same medium
may change between mediums but is accounted for by change in wavelength so that frequency remains
Critical angle equation
@c = sin^-1 ( n2 / n1 )
if wave speed increases what happens to frequency and wavelength?
wavelength increases(directly proporitonal)
frequecny does not change between mediums
lenses and mirrors
if there are six identical chemical cells connected in series...
must add them together.
reduction potential of entire circuit will be sum of the reduction potentials of each
All of the following statements regarding electrochemical cells are true EXCEPT:
A. Electrolytic cells facilitate otherwise nonspontaneous reactions.
B. Electric current always travels from cathode to anode in a galvanic cell.
C. In an electrolytic cell, oxidation reactions are forced to occur at the cathode.
D. The electrode material at the anode of an electrochemical cell is corroded.
C. The passage states that electrolytic cells require energy and are therefore non-spontaneous, eliminating choice A. Electrons travel from the anode to cathode in electrochemical cells. Electrical current, by definition, goes in the direction that a positive ion would travel, and therefore travels from cathode to anode. Choice B is true and also eliminated. The anode is the site of oxidation, and therefore the electrode at the anode will be corroded (solid metal becoming metallic ions), eliminating choice D. The anode is always the site of oxidation, and the cathode is always the site of reduction, irrespective of the type of cell, making choice C a false statement and therefore the correct answer choice.
The atomic mass of boron is 10.8. Boron comes in two naturally occurring isotopes, 10B and 11B. What is the naturally occurring ratio of 10B:11B?
A. Since the weight on the periodic table is an averaged mass, we can write the following equation to solve the question: 10.8 = 11(x) + 10(1 - x). x is equal to the fraction of 11B, and, therefore 1 - x is the fraction of 10B. The equation simplifies to 10.8 - 10 = 11x - 10x, or x = 0.8. Therefore the ratio 10B:11B is 0.2:0.8, or 1:4
10B has an extremely large neutron-capture cross-section, meaning it absorbs free neutrons more effectively than any of the surrounding atoms. However, under conditions of large neutron flux, other atoms may take in neutrons causing instability in their balance of nuclear charge and mass. Which kind of radiation is likely emitted by these atoms to regain this balance?
A. Stable nuclei tend to have the same or slightly more neutrons than protons. If a nucleus becomes unstable as a result of absorbing a neutron, then its mass number is too high and it needs to convert a neutron to a proton. This happens through the emission of a β- particle, which causes the daughter nucleus to maintain mass number but increases the atomic number. Emission of β+particles would convert a proton to a neutron, exacerbating the problem. Emission of γ radiation will not change the mass or the atomic number. The neutral β° particle does not exist.
Ketones can serve as reactive electrophiles if a good Lewis acid is present in solution. Which one of the following reagents is a good Lewis acid?
B. A Lewis acid is a molecule that can accept a pair of nonbonding electrons. These molecules can be recognized easily because they always have a positive charge and/or an incomplete octet. None of the species in choice A, C, or D fit this criterion, but the boron atom in boron trifluoride (choice B) lacks a complete octet
While in motion, a 40 kg child on The Swinging Trapeze experiences a centripetal force of 100 N, while the child's swing traces out a circle of radius 10 m. If this child drops a ball while the ride is in motion, what horizontal distance will the ball travel before it lands, given that he is 10 m above the ground?
A. 4 m
B. 6 m
C. 7 m
D. 9 m
C. The ball is dropping with zero initial y-velocity and an initial x-velocity equal to the velocity of the child. This can be found by using the equation for centripetal force: Fc = mv2 / r. Solving for v gives us pic . The time it takes for the ball to reach the ground is pic . Therefore, the ball will travel 1.4 × 5 = 7 m in the horizontal direction from the place it was dropped.
If the maximum velocity for a swing on The Swinging Trapeze is 2 m/s and the centripetal force on the swing is at least a quarter of the gravitational force acting on the swing, how large can the swing's radius be?
A. 0.8 m
B. 1.6 m Correct Answer
C. It can be as large as you want, it just must be greater than a certain value.
D. You need to know that mass of the person on the swing to determine the radius.
B. Fc must be greater than 1/4 × Fg. As the radius gets larger, the centripetal force decreases; thus there is a maximum size for the radius, not a minimum size (choice C can be eliminated). The mass in the equation cancels out, so choice D is also incorrect.
The stereoconfiguration around the migrating α carbon remains intact during a Baeyer-Villiger oxidation. Therefore, it can be postulated that during the key migration step, this α carbon is:
A. a carbocation.
B. a radical.
C. π bonded to another atom
D. sp3 hybridized having four σ bonds.
D. Unchanged stereoconfiguration implies that the carbon remained chiral throughout the reaction. Choice D is correct because only sp3 hybridized carbons may be chiral.
An atom of beryllium is repelled by an externally produced magnetic field. Which of the following explains this phenomenon?
A. The electrons of beryllium are all spin-paired and the atom is paramagnetic.
B. The electrons of beryllium are not all spin-paired and the atom is paramagnetic.
C. The electrons of beryllium are all spin-paired and the atom is diamagnetic.
D. The electrons of beryllium are not all spin-paired and the atom is diamagnetic.
C. This is a two by two question. First, beryllium's electron configuration is 1s22s2, so all electrons are spin-paired, eliminating choices B and D. Atoms with all electrons spin-paired are diamagnetic, eliminating choice A. Diamagnetic atoms will be repelled by an externally produced magnetic field, and paramagnetic atoms (which have electrons that are not spin-paired) will be attracted to an externally produced magnetic field.
Describe the electric field strength and electric potential at the midpoint between the platform and the satellite.
A. E = 0; φ = 0
B. E ≠ 0; φ = 0
C. E = 0; φ ≠ 0
D. E ≠ 0; φ ≠ 0
C. This could be considered a two-by-two question. Because the point in question is equidistant from identical charges, but in opposite directions, the electric field vectors will superimpose to exactly cancel out. This leaves only choices C or D. Electric potential is a scalar, and for a point charge (which the passage tells us is a good approximation), . The positive contributions from the two charges will add up to a positive, non-zero potential at the midpoint
The satellite's charge is suddenly neutralized, while its momentum and mass remain unchanged. What path will the satellite take?
A. Spiral out into space
B. Continue on instantaneous tangential trajectory
C. Continue on orbit
D. Spiral down toward lunar surface
D. Neutralizing the charge removes the repulsive electric force. Now the only force on the satellite is the gravitational force down. This force is too great for the low, slow orbit of the experiment. The satellite will gradually spiral down toward the moon
A chemist wishes to titrate a sulfuric acid solution. Which base should she use if she wants to be certain that no precipitate will form during the titration?
C. Two substances are produced in a neutralization: water and a salt. In this case a sulfate salt will be produced so we need to find the cation that is soluble when paired with sulfate. Solubility rules tell us Group I metal salts are soluble, and Cs is in Group I. Most inorganic hydroxide compounds are only slightly soluble or insoluble, including all other choices listed
Commercial "concentrated HCl" is a 38% by mass solution in water. Assume the density of concentrated HCl is 1.12 g/mL, what is the molarity of such a solution?
A. 2 M
B. 8 M
C. 12 M
D. 20 M
C. Assume there is 1 mL of solution, which will weigh 1.12 g at the given density. Since the solution is 38% HCl by weight, there will be approximately 0.4 × 1.12 g or about 0.45 g of HCl in the 1.12 g of solution. This 0.45 g of HCl converts to 0.45 g ÷ 37 g/mol or somewhere around 0.012 g HCl in 1 mL. This equates to about 12 M.
How many p electrons does thalidomide possess? PIC
D. Thalidomide has a total of 18 π electrons; 14 from double bonds, and 4 from the two nitrogen lone pairs. Choice A (7) is the number of double bonds. Choice C is the number of π electrons from the double bonds alone.
strong acid and strong base titration
equivalence point: pH=7
if above pH7, weak acid is being titrated
if below 7 weak base is being titrated
rules to determining whether a chemical species will create an acidic, basic or neutral solution
1. The acidity of an element increases as one moves to the right or down the periodic table.
2. The conjugate base (or acid) of a strong acid (or base) forms pH neutral solutions.
3. The conjugate base (or acid) of a weak acid (or base) is a weak base (or acid).
Which of the following compounds would form the least acidic solution when dissolved in water?
The conjugate base (or acid) of a strong acid (or base) forms pH neutral solutions.
FeI3 forms weak acidic
Period of a Spring Pendulum
Why do the seats swing out so that the cables are not vertical?
A. A component of tension must be directed horizontally.
B. A component of gravity must be directed horizontally.
C. Centripetal force pulls the seats out.
D. Centrifugal force pulls the seats out
What is the centripetal acceleration experienced by a passenger during the majority of ride?
A. 0.15 m/s2
B. 0.20 m/s2
C. 0.30 m/s2
D. 0.40 m/s2
If the speed of the swings doubles, what happens to the centripetal force?
A. It increases by less than a factor of 2.
B. It increases by a factor of 2.
C. It increases by more than a factor of 2 but less than a factor of 4.
D. It increases by a factor of 4.
A. Centripetal force acts into the center of the circular path of the swing, so choice C can be eliminated. Centrifugal force is a pseudo-force, not a real force, so choice D can be eliminated. In order to have uniform circular motion, there must be some component of a real force acting into the circle. Of the two options, tension is the only force that can act into the circle, since gravity acts vertically, so choice A is the correct answer
C. ac = v2 / r. From the passage, it is known that v = 2 m/s. The radius must account for the increased distance of the swing from the axis of rotation when the angle θ is increased, so r = 10 + 6 sin30° = 13 m. Thus, ac = (2 m/s)2 / 13 m = 0.3 m/s2.
C. Since Fc = mv2 / r, it is tempting to select D as the answer since Fc is proportional to v2, so from the contribution of the speed increase alone, Fc will increase by a factor of 4. However, from the passage, it is also known that as the speed increases, θ will also increase, thus increasing r. Since the length of the suspension cables is less than the distance of the swing from the center of the axis of rotation, r will increase by a factor that is less than 2 (and greater than 1). Therefore, since Fc is also proportional to 1/r, the total impact on Fc will be an increase by a factor between 2 and 4
graohs wrt pH or Pkas will look like
non linear since logs
Aside from mercury, all transition metal elements have higher melting points than Group I metals. Which of the following best explains this?
A. Transition metal elements can have both d and s electrons delocalized.
B. Transition metal elements are heavier than Group I metals.
C. Group I metal elements are less stable at higher temperatures.
D. Group I metal elements have more valence electrons than transition metal elements.
A. The passage states that "atoms with more delocalized electrons experience greater electrostatic forces with other atoms" which would lead to a higher melting point. Because Group I metals have only one s electron for delocalization and transition metals have both the s and d electrons for delocalization, transition metal elements will have a higher melting point. The heavier Group I metals have melting points lower than lighter transition metals, eliminating choice B. The "stability" of an element is not really well defined, and in any case not related to its melting point, eliminating choice C. The valence of transition metals is not readily determined from the periodic table group and can vary depending on whether or not both s and d electrons are counted. However, transition metal valence certainly can exceed the fixed valence of 1 for Group I metals, eliminating choice D.
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