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Physics Final Exam (Fall)
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Gravity
Terms in this set (76)
displacement
vector quantity that represents a change in position. Also used to describe the difference between an object's initial and final positions. Measured in meters (m)
distance
how much ground an object has covered during its motion
velocity
the rate and direction of the change in the position of an object (vector quantity)
speed
the rate at which an object covers distance
accelaration
rate of change of velocity
vector
Mathematical tool used in physics that has both a magnitude and a direction
displacement equation
xf = xi + d
d = x = xf - xi
velocity equation
v = d/t
v = x/t
instantaneous velocity
speed of an object at a particular instant in time
average velocity
total displacement divided by total time
acceleration equation
a = v/t
object in free fall equation
Vf = Vi + gt
Ball A is dropped from rest from a window. At the same time, ball B is thrown downward; and ball C is thrown upward from the same window. Which statement concerning the balls is necessarily true?
a) all three balls strike the ground at the same time
b) all three balls have the same velocity
c) all three balls have the same acceleration at all times
d) at some instant after it is thrown, the acceleration of ball C is zero
e) all three balls reach the ground with the same velocity
c) all three balls have the same acceleration at all times
for which of the following situations would the path length (distance traveled) equal the magnitude of the displacement?
a) a person walks in and out of every store in a shopping mall
b) a ball is thrown straight up in the air and comes back and hits the ground
c) a train travels 5 miles east; and then, it stops and travels 2 miles west
d) a ball rolls down an inclined plane
e) a jogger runs two laps around a track
d) a ball rolls down an inclined plane
force
action on a body that causes change in motion. measured in newtons (N). Vector quantity.
weight
downward-acting force created by gravity acting on the mass of an object. Measured in newtons or pounds
Free Body Diagram
sketch that isolates a single object and uses arrows to represent the strength, location, and direction of all forces acting on the object.
Normal Force
force perpendicular to a surface. Typically created where objects touch other objects or surfaces, such as floors or walls.
net force
combination of all the forces that act on a body
Equilibrium
state of a system in which all forces are in balance and there is zero net force.
Newton's 1st Law
an object at rest remains at rest, and an object in motion continues with constant velocity, unless acted on by a net force.
Newton's 2nd Law
acceleration of an object is proportional to the net force acting on it and inversely proportional to its mass.
equation for Newton's 2nd Law
F = ma or a = f/m
Things to remember for 2nd law:
1) Always remember that the F appearing in the second law is the net force.
2) The second law is a vector relationship and the direction of acceleration a is the same as the direction of the net force F.
3) If the motion is constrained, such as along a ramp, then the net force will always be along the allowed direction of motion.
Newton's 3rd law
whenever one object exerts a force on another object, the second object exerts an equal and opposite force on the first object.
spring
elastic device specifically designed to produce a controllable restoring force when it is deformed.
Hooke's Law
restoring force of a spring is proportional to the displacement (extension or compression) of the spring. Usually expressed as F = −kx, where k is the spring constant and x is the displacement. Tells us the force from the spring. It is a reaction force to the force exerted on the spring that stretches or compresses the spring.
Elasticity
property of a material to bend or deform without breaking.
static friction
friction force that occurs between two surfaces that are at rest with respect to each other. Equation is Ff = Us*FN
kinetic friction
ratio of the force of dry sliding friction between moving surfaces divided by the normal force acting between the surfaces. Equation is Ff = Uk*FN and is always true if the object is moving.
A rock is thrown straight up from the earth's surface. Which one of the following statements concerning the net force acting on the rock at the top of its path is true?
a) it is equal to the weight of the rock
b) its direction changes from up to down
c) it is instantaneously equal to zero newtons
d) it is greater than the weight of the rock
e) it is less than the weight of the rock, but greater than zero newtons
a) it is equal to the weight of the rock
A 2.0-N rock slides on a frictionless inclined plane. Where does the normal force point?
a) straight up
b) straight down
c) at an angle to the left and upward
d) to the left
e) to the right
c) at an angle to the left and upward
under what condition(s) will an object be in equilibrium?
a) only if it is at rest
b) only if it is moving with constant acceleration
c) only if it is moving with constant velocity
d) if it is either at rest or moving with with constant velocity
e) if it is either moving with constant velocity or with constant acceleration
d) if it is either at rest or moving with with constant velocity
A man tries to push a 500N crate horizontally across a rough surface, but it does not move. He pushes with a force of 250N. What is the frictional force that the floor applies to the crate in this situation?
-250N
A 70kg astronaut pushes to the left on a spacecraft with a force F in "gravity free" space. The spacecraft has a total mass of 10,000kg.
Which of the following statements concerning this situation is true?
a) the astronaut does not move
b) the force exerted on the astronaut is larger
c) the acceleration of the astronaut is larger
d) the acceleration of the spacecraft is larger
e) the force exerted on the spacecraft is larger
c) the acceleration of the astronaut is larger
A man pushes down on the earth. What happens as a result of this force?
a) the earth pulls the the astronaut back towards the earth
b) the earth pushes the astronaut up away from the earth
c) the moon pulls the man away from the earth
d) the man pulls the earth up toward him
e) the man pushes the earth down away from him
b) the earth pushes the astronaut up away from the earth
A hunter on the ground fires a tranquilizing dart at a monkey hanging in a tree in the distance. However, this is a special monkey with amazing reflexes. As soon as the hunter fires, the monkey will let go of the tree and fall to the ground. Where should the hunter aim to hit the monkey?
at the monkey
a projectile is fired from a gun and has initial horizontal and vertical components of velocity equal to 30m/s and 40m/s, respectively. What is the acceleration of the projectile when it reaches its maximum height?
9.8m/s downward
Ball A is thrown horizontally out of a window. Ball B is dropped from the window. Ball C is thrown straight up from the window, and ball D is thrown straight down from the window. Assuming they are all thrown with the same speed, in what order will they hit the ground?
D, B&A, C
A ball is placed on a frictionless ramp at an angle of 45 degrees. Which of the following is true?
a) the ball will accelerate at a rate of 0m/s^2
b) the ball will accelerate at a rate of 9.8m/s^2
c) the ball will accelerate at a rate that is between 0 and 9.8m/s^2
d) the ball will accelerate at a rate that is greater than 9.8m/s^2
e) the ball will accelerate at a rate that is less than 0m/s^2
c) the ball will accelerate at a rate that is between 0 and 9.8m/s^2
How do we find the magnitude of a resultant vector is we know the components?
use Pythagorean theorem of the x and y components as the sides of the triangle
if the distance between the centers of two objects is doubled, the gravitational force between them
a) increases by a factor of 2
b) decreases by a factor of 2
c) increases by a factor of 4
d) decreases by a factor of 4
e) does not change
a) increases by a factor of 2
When trying to find how fast a planet is in orbit, which of the following do we NOT need to know?
a) universal gravity constant
b) how far away the planet is from the star
c) mass of the planet
d) mass of the star its orbiting
e) we need to know all of these to determine orbital speed
c) mass of the planet
Which of the following will produce the most torque?
a) a large force close to the axis of rotation
b) a small force close to the axis of rotation
c) a large force far away from the axis of rotation
d) a small force far away from the axis of rotation
e) all of them will produce the same torque
c) a large force far away from the axis of rotation
If the mass of the earth was doubled, what would happen to the weight of every person on the planet?
a) increases by a factor of 2
b) decreases by a factor of 2
c) increases by a factor of 4
d) decreases by a factor of 4
e) does not change
a) increases by a factor of 2
mechanical energy
energy that comes from position or motion. Gravitational potential energy, elastic potential energy, rotational energy, and kinetic energy are examples
radiant energy
includes visible light, microwaves, radio waves, x-rays, and other forms of electromagnetic waves.
nuclear energy
sometimes called atomic energy, is energy contained in matter itself
electrical energy
moves in the form of electric currents that flow in response to electrical voltages, such as in a battery or wall socket
chemical energy
stored in the bonds between the constituent atoms in molecules that make up most matter
thermal energy
another word for heat; energy that is attributed to an object's temperature
pressure
a consequence of thermodynamic energy—a form of mechanical energy at the microscopic level—that is important in gases and liquids. It takes work to inflate a tire; some of the work is stored as energy in the form of high-pressure air inside the tire. This is a form of Potential, or stored, energy.
work
a form of energy equal to one newton of force exerted for one meter in the direction of the force. Measured in joules (J).
kinetic energy
energy due to mass in motion. Measured in units of joules (J)
potential energy
energy of position—often due to gravity, but also includes other forms such as elastic potential energy and pressure. Measured in joules (J). Two main types, gravitational and Elastic. Potential energy is relative to your starting point. Often called stored energy.
power
rate at which work is done or energy is transferred. The units of power are watts (W). One watt is one joule per second.
light
form of radiant energy consisting of electromagnetic waves traveling at the speed of light. Example would be the energy produced by a light bulb.
horsepower
unit of power equal to 746 watts
renewable energy
comes from natural sources of energy—such as solar, water from rainfall, wind, tides, or geothermal heat—that are replenished naturally and presumably can be used as an energy source indefinitely
solar energy
derives power from the radiant energy in sunlight. Sunlight can be used to heat water for household use; it can be used to create steam, which then powers a turbine; and it can directly generate electric current when absorbed by a photovoltaic cell.
hydroelectric energy
refers to the mechanical energy of water flowing from higher places to lower ones. For centuries, this energy has crushed grain and spun lathes in mills built alongside rivers and waterfalls; today it is used mainly to generate electricity
wind energy
has long been used to pump water or grind grain. Wind energy is today increasingly being tapped to generate electricity. Ultimately, wind derives its power from sunlight and, to a lesser extent, from Earth's rotation.
geothermal energy
thermal energy and pressure contained within underground bodies of water heated by magma—molten rock that rises from deep within the Earth. Hot springs and geysers are two natural geothermal phenomena.
tidal energy
ultimately comes from the gravitational interaction among the Earth, the Moon, and the Sun. This interaction causes ocean water to flow back and forth twice daily. Tides involve tremendous amounts of mechanical energy—energy that is hardly tapped today.
nuclear fusion
derives energy through nuclear reactions that combine lighter elements into heavier elements. Nuclear fusion is the energy source for the Sun and stars. A practical fusion reactor, however, has yet to be developed. (The opposite process, nuclear fission, powers today's nuclear plants.)
a solar panel's main purpose is to turn ....... energy into .......... energy
a) mechanical, electrical
b) nuclear, mechanical
c) chemical, theraml
d) thermal, mechanical
e) radiant, electrical
e) radiant, electrical
a solid metal ball and a hollow plastic ball (smaller mass) of the same external radius are released from rest in a large vacuum chamber. When each has fallen 1m, they both have the same
a) potential energy
b) kinetic energy
c) power
d) speed
e) mass
d) speed
Georgia Power charges its customers for the amount of kW*h they use. This is a unit of what quantity?
a) power
b) energy
c) electricity
d) current
e) voltage
b) energy
a man jumps out of an airplane. if we neglect air resistance, which of the following is true?
a) the man turns kinetic energy into potential energy as he falls
b) the man turns potential energy into kinetic energy as he falls
c) the man does positive work as he falls
d) gravity does no work on him as he falls
e) the man uses elastic potential energy
b) the man turns potential energy into kinetic energy as he falls
system
group of related and interacting objects and influences that we choose to investigate; can be open or closed
closed system
isolated system that cannot exchange matter or energy with its surroundings.
open system
system on which outside influences can act, such that matter or energy can be added or removed from the system.
law of conservation of energy
total energy in a closed system does not change over time. While energy cannot be created or destroyed, it can be transformed from one form to another, just as long as the total energy remains constant.
work-energy theorem
change in the kinetic energy of an object equals the net work done on it.
positive work
puts energy into the system, increase KE
negative work
removes energy from the system, decrease KE
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