physcis energy test
Two identical objects in outer space have a head-on collision and stick together. If, before the collision, one had been moving at 2 m/s and the other at 1 m/s, their combined speed after the collision would be
.5 m/s
The power required to exert 1 N force, over a distance of 1 m in 1 second is
1 W
It takes 40 J to push a large box 4 m across a floor. Assuming the push is in the same direction as the move, what is the magnitude of the force on the box?
10 N
A machine puts out 100 Watts of power for every 1000 Watts put into it. The efficiency of the machine is
10%
Neglecting air resistance, a man on a high ladder releases a ball which strikes the ground with 100 J of kinetic energy. If he were to throw it straight upward instead, it will eventually reach the ground with a kinetic energy of
100J
Two identical 5000-kg bulldozers roll toward each other on a level road without friction (one at 1 m/s, the other at 2 m/s) Just before they collide, one has a kinetic energy of 2500 J and the other 10,000 J. At this instant their total kinetic energy is
12,500 J
A car moves 4 times as fast as another identical car. Compared to the slower car, the faster car has
16 times the KE.
A car moving at 50 km/hr skids 20 m with locked brakes. How far will the car skid with locked brakes if it were traveling at 150 km/hr?
180 m
Do 100 J of work in 50 s and your power output is
2 W
A 2500-N pile-driver ram falls 10 m and drives a post 0.1 m into the ground. The average impact force on the ram is
250,000 N.
A 2 kg mass has 40 J of potential energy with respect to the ground. Approximately how high is it above the ground?
2m
A motorcycle with a mass of 100 kilograms slowly rolls over the edge of a cliff and falls for three seconds before it reaches the bottom of a gully. Its momentum (in units of kilogram meters per second) just before it hit bottom and became burned rubber and scrap metal was
3,000.
How many Joules of energy are in one kilowatt-hour?
3.6 million
A TV set is pushed a distance of 2 m with a force of 20 N. How much work is done on the set?
40 J
A bow is drawn so that it has 40 J of potential energy. When fired, the arrow will ideally have a kinetic energy that is
40 J.
Suppose a miracle car has a 100% efficient engine and burns fuel that has a 40-megajoules-per-liter energy content. If the air drag and overall frictional forces on this car traveling at highway speeds total 1000 N, what is the overall limit in distance per liter it could be driven on the highway?
40 km
A piece of taffy slams into and sticks to another identical piece of taffy that is at rest. The momentum of the two pieces stuck together after the collision is the same as it was before the collision, but this is not true of the kinetic energy, which is partly turned into heat. What percentage of the kinetic energy is turned into heat?
50 %
Using 1000 J of work, a toy elevator is raised from the ground floor to the second floor in 20 seconds. The power needed to do this job was
50 W
A jack system will increase the potential energy of a heavy load by 1000 J with a work input of 2000 J. The efficiency of the jack system is
50%
A diver who weighs 500 N steps off a diving board that is 10 m above the water. The diver hits the water with kinetic energy of
5000 J
Two 5000-kg passenger cars roll without friction (one at 1 m/s, the other at 2 m/s) toward each other on a level track. They collide, couple, and roll away together with a combined momentum of
5000 kg m/s
A car's engine is 20% efficient. When cruising, the car encounters an average retarding force of 1000 N. If the energy content of gasoline is 40 megajoules per liter, how many kilometers per liter does the car get?
8
A 2-kg mass is held 4 m above the ground. What is the approximate potential energy of the mass with respect to the ground?
80 J
Consider a hydraulic press. When the input piston is depressed 20 cm, the output piston is raised 1 cm. On the same press, an input force of 1 N can lift a load of
All of the above are correct.
A car has a head-on collision with another car that was approaching with the same magnitude of momentum. A third identical car driving with the same speed as the first car runs into an enormously massive wall. Which of the four objects will experience the greatest impulse?
All will receive the same impulse.
What task requires the most work; lifting a 50-kg sack 2 meters or lifting a 25-kg sack 4 meters?
Both require the same amount of work.
A flower pot of mass m falls from rest to the ground below, a distance h. Which statement is correct?
The KE of the pot when it hits the ground is proportional to h.
Compared to the recoiling rifle, the bullet fired has
a greater kinetic energy
If several balls are thrown straight up with varying initial velocities, the quantity that will have the same value for each trial is the ball's
acceleration.
a feather and a coin dropped in a vacuum fall with equal
accelerations
a heavy and a light object released from the same height in a vacuum have equal
accelerations.
a moving object has
all of these
A hydraulic press, like an inclined plane, is capable of increasing energy.
always false
When properly used, a hydraulic press, like a wheel and axle, is capable of multiplying force input.
always true
A pile driver hits the top of a telephone pole, driving it partway into the ground. The distance that the pole will sink into the ground depends on
any of the above choices
When a rifle is fired, it recoils as the bullet is set in motion. The rifle and bullet ideally acquire equal
but opposite amounts of momentum.
When bullets are fired from an airplane in the forward direction, the momentum of the airplane will be
decreased.
An open freight car rolls friction free along a horizontal track in a pouring rain that falls vertically. As water accumulates in the car, the car's speed
decreases
Whereas impulse involves the time that a force acts, work involves the
distance that force acts.
A popular swinging-balls apparatus consists of an aligned row of identical elastic balls that are suspended by strings so they barely touch each other. When two balls are lifted from one end and released, they strike the row and two balls pop out from the other end. If instead one ball popped out with twice the speed of the two, this would be a violation of conservation of
energy
Two pool balls, each moving at 2 m/s, roll toward each other and collide. Suppose after bouncing apart, each moves at 4 m/s. This collision violates conservation of
energy
The total momentum of a flock of identical birds could be zero only if the birds are
flying in different directions.
A car that travels twice as fast as another when braking to a stop will skid
four times as far.
Two identical arrows, one with twice the speed of the other, are fired into a hay bale. The faster arrow will penetrate
four times further than the slower arrow.
A clerk can lift containers a vertical distance of 1 meter or can roll them up a 2 meter-long ramp to the same elevation. With the ramp, the applied force required is about
half as much.
When an automobile is braked to a stop, its kinetic energy is transformed to
heat
A ball is projected into the air with 100 J of kinetic energy which is transformed to gravitational potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is
less than 100 J.
An object may have potential energy because of its
location
A bullet has more kinetic energy than the recoiling rifle from which it is fired is because the force on the bullet acts over a
longer distance
If an object has kinetic energy, then it also must have
momentum
If the speed of a moving object doubles, which of the following also doubles?
momentum
A golf ball is thrown at and bounces backward from a massive bowling ball that is initially at rest. After the collision, compared to the golf ball, the bowling ball has
more momentum, but less kinetic energy.
A 1-kg ball dropped from a height of 2 m rebounds only 1.5 m after hitting the ground. The amount of energy converted to heat is about
more than 2.0 J
If a ping pong ball and a golf ball are both moving in the same direction with the same amount of kinetic energy, the speed of the ping pong ball must be
more than the golf ball.
An object that has kinetic energy must be
moving.
A ball rolling down an incline has its minimum speed
near the top of the incline.
If you push for a half hour or a whole hour against a stationary wall
no work on the wall is done in either case.
A woman carries a heavy box across a room at a constant speed. How much work does she do on the box while walking?
none
A light aluminum ball and a heavy lead ball of the same size are allowed to roll down an incline. When they are halfway down the incline, they will have identical
none of the above choices
When an object is in motion, which of the following could not have a value of zero.
none of the above could be zero.
an object at rest may also have
potential energy
A job is done slowly, while an identical job is done quickly. Both jobs require the same amount of work, but different amounts of
power
Which requires the most amount of work by the brakes of a car?
slowing down from 100 km/h to 70 km/h.
Which has greater kinetic energy, a car traveling at 30 km/hr or a car of half the mass traveling at 60 km/hr?
the 60 km/hr car
A ball rolling down an incline has its maximum kinetic energy at
the bottom
A block of ice sliding down an incline has its maximum speed at
the bottom
Two identical freight cars roll without friction (one at 1 m/s, the other at 2 m/s) toward each other on a level track. They collide, couple together, and roll away in the direction that
the faster car was initially going
No work is done by gravity on a bowling ball that rolls along a bowling alley because
the force on the ball is at right angles to the ball's motion.
Both a 50-kg sack is lifted 2 meters from the ground and a 25-kg sack is lifted 4 meters in the same time. The power expended in raising the 50-kg sack is
the same
After rolling halfway down an incline, a marble's kinetic energy is
the same as its potential energy.
The ball rolling down an incline has its maximum potential energy at
the top
If you do work on an object in one-third the usual time, your power output is
three times the usual power output.
Strictly speaking, more fuel is consumed by your car if an air conditioner, headlights, or even a radio is turned on. This statement is
true.
Two identical arrows, one with twice the kinetic energy of the other, are fired into a hay bale. The faster arrow will penetrate
twice as far as the slower arrow.
If an object is raised twice as high, its potential energy will be
twice as much
If you push an object twice as far while applying the same force, you do
twice as much work
A 1000-kg car and a 2000-kg car are hoisted the same distance. Raising the more massive car requires
twice as much work.
If you push an object a given distance, while applying twice the force, you do
twice as much work.
One end of a long, uniform log is raised to shoulder level. Another identical log is raised at its center to the same level. Raising the second log requires about
twice as much work.
An object lifted 10 meters gains 200 J of potential energy. If the same object is lifted 20 meters, its potential energy gain is
twice as much.
If you find that twice as much work is needed to perform a task but it takes twice as much time, the amount of power required is
unchanged
