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a woman carries a heavy box across a room at a constant speed. how much work does she do on the box while walking?
when a rifle is fired it recoils as the bullet is set in motion. The rifle and bullet ideally acquire equal
amounts of energy but opposite amounts of momentum
the total momentum of a flock of identical birds could be zero only if the birds are
flying in different directions
if you push for a half hour or a whole hour against a stationary wall
no work is done on either case
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
two identicial arrows, one with twice the speed of the other, are fired into a hay bale. the faster arrow will penetrate
four times as far as the slower arrow
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 you do work on an object in one-third the usual time, your power output is
three times the usual power output.
a car moves 4 times as fast as another identical car. compared to the slower car the faster car has
16 times the kinetic energy
if you find that twice as much work is needed to perform a task but it takes as much time, the amount of power required is
a 1000-kg car and a 200-kg car are hoisted the same distance. raising the more massive car requires
twice as much work
which has a greater kinetic energy, a car traveling at 30 km/hr of a car of half the mass traveling at 60 km/hr
the 60 km/hr car
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
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
it takes 40 J to push a large box 4 m across a floor. assuming the push is the same direction as the move, what is the magnitude of the force on the box
a machine puts out 100 watts of power for every 1000 watts put into it. the efficiency of the machine is
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
a 2 kg mass has 40 J of potential energy with respect to the ground. Approximately how high is it above the ground
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
a pully system raises a 1000-N load 2 meters with 100 N of input force. The efficiency of the system is
not enough information given
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
two identical 5000-kg bulldozers roll toward each other on a level road without friction (one at 1m/s, the other at 2m/s) just before they collide, one has a kinetic energy of 2500 J and the other 10000J this instant their total kinetic energy is
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
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
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
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
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