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ps 303
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Gravity
question from the entire semester
Terms in this set (67)
friction
the resistive force that opposes the motion or attempted motion of an object it is a negative force and the friction is dependent on it's surface
mass
the quantity of matter in an object it measure the inertia an object exhibits in response to any effort to change the state of motion
weight
the force due to gravity on an object [ -m(9.8) ]
Newton
the SI unit of force
kilogram
is the SI unit for mass
force
any influence that can cause an object to be accelerated, measured in newtons
free fall
motion under the influence of gravitational force [-9.8 ]
how does friction affect the net force on a object?
by creating an negative force to get the sum of all forces
what relationship does mass have with inertia?
mass is the measurement of inertia
Consider a car that has a 100% of efficient engine and burns fuel that has an energy content of 40 mega joules per liter. if the air drag and overall friction forces on the car traveling at highway speed is 500 N, how far could be car travel per liter of fuel at this speed? hint: Work= Force x Distance
80 km/ L
work
the product of the force and the distance moved by the force W=Fd
Power
the time rate of the work P= W/ T
Energy
the property of a system is the rate at which energy is work
potential energy
the energy that something possesses because of its position -- usually the object on a vertical surface or have up/ down direction -- Ep= mgh
kinetic energy
the work done on an object equals the change in the kinetic energy of the -- usually on a horizontal surface -- Ek= 1/2mv²
Conservation of energy
energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes.
which requires more work--lifting a 50 kg sack a vertical distance of 2m or lifting a 25kg sack vertical distance 4m?
lifting a 25 kg sack 4m
calculate the work done when a force of 1 N moves a book 2m
W = 2 J
calculate the work done when 20 N force pushes a cart 3.5m
W = 20 x 3.5-- J
calculate the work done in lifting a 500 N barbell 2.2 m above the floor.
W = 500 x 2.2 -- J
how many joules of potential energy does 1-kg book gain when it is elevated 4 m? when it is elevated 8m?
Ep = 1x9.8x4 = J
Ep = 1x9.8x8 = J
calculate the increase in potential energy when a 20 kg of water of ice life a vertical distance of 2m.
Ep = 20x9.8x2 = J
calculate the change in potential energy of 8 thousand kg of water dropping 50 m over niagara falls
Ep= 8, 000x -9.8x 50m
True of False: A vector is a large quantity and a scalar is a small quantity
False: Vector or scalar quantities vary
True or False: a vector quantity is described, besides magnitude, with a direction and a scalar is not
True: vectors have two things and scalar just have one
True or False: position is a vector quantity and displace is a scalar quantity
False: Displacement is a vector
True of False: a person makes a round-trip journey, finishing where she started. the displacement for the trip is 0 m.
True:
True or False: the expression "20 m" describes the displacement for motion
False: Displacement is a vector
Originally, a pendulum oscillates 12 times in one second.
A) what is the period
b) if we increase the mass of the pendulum, what happens with its period?
c) if we decrease the length of the pendulum, what happened with the number of oscillations in one second?
d) if we double the period of the pendulum, how many times would it oscillate in 1 min?
a) .083 s
b) if we increase the mass of the pendulum their will not be a significant difference in change for the pendulum period
c) if we decrease the length of the pendulum the number of oscillations in one second will increase in the number of the periods. the less traveled the more periods it can have
d)360
an object moves on a horizontal plane with a = 2 m/s^2. Say if the following statements about the object are true or false:
a) the kinetic energy of the object is constant
b) the potential energy of the object is constant
c) there is work being done upon the object
a) False: because it is on a horizontal plane
b) True: because it is constant therefore the net force is zero
c) True: because it is accelerating
a joule is the unit to measure work in the SI. If work is defined as W=Fd, one joule is equivalent to what?
kgm²/ s²
Two boxes are seen to accelerate at the same rate when a force 3F is applied to the first and 2F is applied to the second. What is the mass ratio (M1/ M2) of the boxes.
3/2
if a golf ball and ping pong ball both move with the same kinetic energy, can you say which has greater velocity? explain
(1/2)(big mass)(small velocity)² = (1/2)(small mass)(big velocity)²
when the velocity of an object is divided by 3, by what factor is its kinetic energy changed?
Ke= 1/9 (1/2xMxV²)
Suppose the Earth travels around the Sun with constant speed. Answer the following questions:
a) is the velocity of the Earth the same on March the 21st as on September the 21st?
b) is there any force acting on the Earth/ How do you know?
a) no because the direction changed and velocity is a vector
b) yes - gravity [ -m(9.8) ]
what is the net force on a .3kg apple when you hold it at rest above your head? What is the net force on it after you release it?
a) zero: because there is no acceleration
b) [-3(9.8)] N
is it possible for an object to be under a constant net force action and have constant speed?
no because if there is constant velocity then the net force will always equal zero because there has to be some acceleration
a sphere with M = 10kg is thrown upward, from the ground, with initial speed v=20 m/s. calculate the max height it reaches
h= 2000/ 10 (9.8)
If there is an object with constant accelereation on a surface and there is a string pulling horizontally; it is always true there is friction force involved
False: it depends on the situation-- some surfaces do not cause friction
if a force is acting on a body, the direction of the motion (velocity) and the direction of the force are always the same.
False: No because the acceleration and the force direction not the velocity is the same
if there is no air resistance and you drop two object, one four time as heavy as the other, the heaviest will fall with the double of acceleration.
False: the acceleration will not double because the objects will just have a gravitational force that is the same 9.8 and it will be negative since it is going down
if an object is moving, there is always a force acting on it
True: force is the result of an object moving; something has to accelerate moving objects and that's force
when a body is falling and there is are resistance, the potential energy that the object loses is the same as the work that the air friction dose on an object
False: because Ep= mgh and friction is the amount of positive resistance that is on the object
if you are pushing an object on a surface and there is friction and the object moves with constant velocity; it is true that if you increase the mass of the object, the work done by the surface will decrease.
False: no the work done by the surface will remain the same
a rock that weighs 20 N is released from a position 20m high. When it strikes the ground. it stops after .oo1 seconds. what is the magnitude of the force that the ground exerts on the rock
Force= 48000 N
if the mass of a sliding block is somehow tripled at the same tome the net force is tripled, how does the resulting acceleration compare with the original acceleration
af= fi/ mi
write in basic units:
Force x acceleration/ time
ask someone in class?
energy x time² x distance
ask someone in class?
How much net force is required to keep a 10 kg object moving rightward with a constant velocity of 2m/s²? Explain
net force = zero
when there is constant velocity there is no acceleration, therefore it will be zero because net force = m x a
an airplane releases an object from a height of 1.5 km above the ground. irgnoring any air resistance find:
a)the time that it takes to the object to hit the ground
b)the vertical velocity that the object has right before it hits the ground
a)17.50 s
b) change in velocity = - 53.1356 m/s
a tow truck exerts a a16500 N force upon a 1429 kg car to drag it out of a mud puddle onto the shoulder of a road. A15500 N force opposes the car's motion. The Plane of motion of the car is horizontal.
a)find the acceleration
b)determine the time required to drag the car a distance of 6.90 meters from its rest position.
a = .70
t= 4.44s
All objects have inertia
true
acceleration and net force have always the same direction
true
the weight of an object is dependent upon the value of the acceleration of gravity
true
inertia is a force
false
if an object is moving to the right and slowing down, then the net force on the object is directed towards the left
true because there is friction form the left that is slowing it down
two objects of the same mass can weigh differently on the Earth surface.
no because weight is -m(9.8)
when a object is in free fall, the net force acting on it is zero
false because it still has a 9.8 deceleration - where there is acceleration the net force is not zero
what is the speed for a horse that gallops a distance of 15km in a time of 30 min?
s= 8.3 m/s
determine the position in meters, at t= 20s, os an object which moves in the north direction:
A) is at the origin when t = 30s and is moving with constant v= 4.5 m/s
b) is at the origin when t = 0.0s and at 4 m from the origin when t= 2.5s and moves with constant velocity
a) position = 76.5 m
b) position = 32 m
Th ocean's level is currently rising at about 2.5 millimeters per year. At this rate in how many years will sea level be 2m higher
800 years
the slop of the velocity v. time graph gives you the speed of motion
False it gives you the acceleration or position
if the direction of motion changes, the speed changes
false the velocity is different but the speed can be the same with a different direction because velocity is a vector
the units for mass in the international system SI are grams
false it is kg kilograms
if someone is driving with constant speed it is true that:
he could be traveling in a curved path
determine the final velocity in meters, at t=25.0s, of an object which:
a) at t= 0 is moving with V= 3.0 m/s and increases its velocity 2 m/s every 4.0s
b) at t= 0 is at rest (velocity = 0 m/s), and changes it velocity 2.5 m/s in 1s
a)12.5 m/s
b) 62.5 m/s
determine the acceleration in m/s² of an object which:
a) moves in a straight line with a constant speed of 20.0 m/s for 12.0 seconds
b) changes its velocity from 60.0 km/h to 0.00 km/h in 4 seconds
c)changes its velocity from 12 m.s to 23,5 m/s in 7.8 seconds
a) o m/s²
b)-4.17 m/s²
c)
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