# Physics Ch 7

## Unlock all answers in this set

question
the power required to exert a 4-N force over 3 meters in 2 seconds is
4(3)=12/2= 6 6 W
question
the work you do when pushing a shopping cart twice as far while applying twice the force is
four times as much
question
hydro and wind power are indirect forms of
solar energy
question
a roller skate at rest may have
energy
question
relative to an initial height, an object raised twice as high has a gravitational potential energy that is
twice as much
question
when Joshua brakes his speeding bicycle to a stop, kinetic energy is transformed to
heat
question
a hydraulic jack is used to lift objects such as automobiles. If the input force is 200 N over a distance of 1 meter, the output force over a distance of 0.1 meter is ideally
f x d 200(1)=f(.1) 200/.1=2000 2000 N
question
an object that has kinetic energy must be
moving
question
a 2 kg ball is held 4m about the ground. Relative to the ground its potential energy is
question
two identical arrows, one with twice the speed of the other, are fired into a bale of hay. Compared with penetration of the slow arrow, the faster arrow penetrates
four times as far
question
which task requires more work a. lifting the 25 kg sack 4 meters b. both the same c. lifting the 50 kg sack 2 meters d. need more information
B. both the same
question
the power expended doing 100J of work in 50 s is
2 W
question
a crate of grapes lifted 10 meters gains 200 J of potential energy. If the same crate is instead lifted 20 meters, its gain in potential energy is
twice as much
question
a machine puts out 100 watts of power for every 1000 watts put into it. The efficiency of the machine is
100/1000=.1= 10%
question
a ball rolling down an incline has its maximum kinetic energy at
the bottom
question
if a ping pong ball and a golf ball both move 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
question
two identical arrows, one with twice the kinetic energy of the other, are fired into a bale of hay. Compared with penetration of the slow arrow, the faster arrow penetrates
twice as far
question
a hydraulic press has its input piston depressed 20 cm while the output piston is raised 1 cm. A 1 N input can lift a load of
20 N
question
which has greater kinetic energy a. a car half the mass traveling at 60 km/hr b. need more information c. a car traveling at 30 km/hr d. both the same
a. a car half the mass traveling at 60km/hr
question
a 2 kg box of taffy candy has 40 J of potential energy relative to the ground. Its height above the ground is
PE= mgh 2(10)(h)=40 20=40 40/20=2 2 m
question
danny diver weighs 500 N and steps off a diving board 10 m above the water. Danny hits the water with kinetic energy of
more than 5000 J
question
about 40 J is required to push a crate 4 m across a floor. If the push is in the same direction as the motion of the crate, the force on the crate is about
10 N
question
a ball rolling down an incline has its maximum potential energy at
the top
question
an object has gravitational potential energy due to its
location
question
a primary difference between momentum and kinetic energy is
momentum can cancel; KE energy cannot
question
strictly speaking, more fuel is consumed by your car if the air conditioner, headlights, or even a radio is turned on. This statement is
true only if the car's engine is running
question
when wind encounters a wind turbine that produces energy, wind speed on the downside of the blades is
speed up
question
phil applies 100 N to a pulley system and raises a load one-tenth of his downward pull. Ideally, the weight of the load is
1000 N
question
a toy elevator is raised from the ground floor to the second floor in 20 seconds. The power needed using 1000 J of work is
1000/20 50 W
question
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
50(2)=100 25(4)= 100 the same
question
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
1000/2000=.5=50% 50%
question
a clerk can lift cylindrical packages 1 meter vertically, 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
question
two identical golf carts move at different speeds. The faster cart has twice the speed and therefore has
four times the kinetic energy
question
the work you do when pushing a shopping cart a given distance while applying twice as much force is
four times as much
question
when a drawn bow of potential energy 40 J is fired, the arrow will ideally have a kinetic energy
more than 40 J
question
the work you do when pushing a shopping cart twice as far while applying the same force is
twice as much
question
the bob of a simple pendulum has its maximum kinetic energy at the
bottom of its swing
question
a 1000 kg car and a 200 kg car are hoisted to the same height. Raising the more massive requires
twice as much work
question
two 2-m/s pool balls roll toward each other and collide. Suppose after bouncing apart each moves at 4m/s. this collision violates the conservation of
energy
question
a circus diver drops from a high pole into water far below. When he is halfway down a. he has gained an amount of kinetic energy equal to has his initial PE b. none of the choices c. all choices are correct d. his PE is halved e. his KE and PE are equal