Science Test: Energy Unit Test
Calculate the number of joules of KE a .6-kg basketball has when it is inbounded at a speed of 2 m/s.
0.6•4= 1.2
If you push for an hour with 1500-N against a wall and it does not move, how much work is done?
0J
A machine puts out 100 W of power for every 1000 W put into it. The efficiency of the machine is
10 percent
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?
10N
What is the efficiency of a machine that requires 15 J of energy to do 13 J of work?
13/15= 0.866•100= 86.66
A car moves four times as fast as an identical car. Compared to the slower car, the faster car has
16 times the KE
If you exert 100 J in 50 s, your power output is
2 W
A roller coaster has a mass of 375 kg. At the bottom of the first hill it has a velocity of 20 m/s. How much KE does the roller coaster have?
375/ 2 = 187.5 • 400= 75,000
Using 1000 J of work, a toy elevator is raised from the ground floor to the second floor in 20 s. How much power does the elevator use?
50 W
Calculate the power expended when a 5-N force moves a block up a 3-m ramp is 10 s.
5•3/10= 1.5
A TV set is pushed a distance of 2.2 m with a force of 33 N that is in the same direction as the set moves. How much work is done on the set?
72.6j
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
7
Both require the same amount of work
express the law of conservation in energy
Energy cannot be created or destroyed.
Calculate the work done when a force of 5-N moves a block up a ramp a distance of 3 m.
W = 5•3 = 15J
When is work done on an object
When the object is in motion
electric battery
chemical
food
chemical
a compressed string
elastic
a drawn bow with arrow
elastic
a raised wrecking ball
gravitational
a roller coaster at the top of the first hill
gravitational
water in a reservoir
gravitational
What are the two forms of mechanical energy?
kinetic energy and potential energy
An object that has kinetic energy must be
moving
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
Why can't a machine be 100% efficient?
same input is transferred to heat reducing output
A clerk can lift containers a vertical distance of 3 m or can roll them up a 6-m-long ramp to the same elevation. With the ramp, the applied force required is about
twice as much
When an object is lifted 10m, it gains a certain amount of potential energy. If the same object is lifted 20m, it's potential energy gain is
twice as much
If you push an object twice as far while applying the same force, you do
twice as much work
The same roller coaster has fallen 10-m on the first drop. Using the information from the questions above, what is the PE and KE of the roller coaster at this 10-m point in the fall?
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