Name ______Period ______Date ______
Work, Power, Energy Review Sheet
Directions: answer the following using complete sentences
1. What is work?Use your book, p 103. Page 119 is helpful, too,
and the glossary shows this on page 706.
2 When deciding if work has occurred on an object, what must have happened to the object? (two things)
3. What is power?
4. Power measures how quickly you are doing what?
5. What must an object have if it possesses kinetic energy?
6. What is the law of conservation of energy?
Directions: Solve the following. Write the algebraic formula; show all work, answers and units. (Don’t worry about rotational kinetic energy.)
7. An object (m = 1.5 kg) is pushed across a floor with an acceleration of 4 m/s2 for a distance of 10 m in 3.5 seconds. How much work was done on the object? What is the power output?
Work = F x dRecognize that you don’t use the “m = 1.5 kg”
P = Work/t so divide your work answer by 3.5 s
8. A 1500 kg vehicle is moving with a velocity of 12 m/s on smooth asphalt. When the driver decides to drive through the mud, the velocity slows to 10.0 m/s. Find the work done on the vehicle that caused it to slow down.
Work = KE so Work = KE f – KE I Find the KE at the final speed and subtract
= .5 mvf2 - .5 mvi2 the KE at the initial speed
It’s OK to have a negative answer.
9. A 5.00 kg remote control toy has an initial velocity of 2.00 m/s and runs into an obstacle. The work done on the car is – 5.00 J. What is the final velocity of the car?
Work = KE so Work = KE f – KE I This time, you are solving for vf.
-5.00 J= .5 mvf2 - .5 mvi2
10. An object (m = 5.0 kg) is pulled with a force of 300.0 N for 9 seconds. The object moved 5.00 m. How much work was done on the object? What was the power output?
Work = F x dRecognize that you don’t use the “m = 5.0 kg”
P = Work/t so divide your work answer by 9 s
11. A person lifts a crate (m = 50.0 kg) straight up into the air for 2.0 seconds. The crate was raised 1.5 m. How much work was done on the crate? What was the person’s power output?Work = F x d but this problem gives you mass. Work = mg x d
P = Work/t so divide your work answer by time
12. A person lifts a box (m = 300. g) straight up for 1.5 seconds. The box reached a height of 1.8 m. How much work was done on the box? What was the person’s power output?
Work = F x d but this problem gives you mass. Work = mg x d
P = Work/t so divide your work answer by time
13. A skydiver (m = 100. kg) is as about to practice by jumping out of a tower that is 15 m high. What is the person’s potential energy at the top of the tower?
PE = mghPE = mass x 9.8 x that tower’s height
14. Tony Romo throws a football (m = 0.80 kg) with a velocity of 25 m/s. What is the kinetic energy of the football?
KE =.5 mv2KE = .5 x mass x velocity squared
15. Find the velocity of the ball at points A,B, and C if the ball originally started from rest on top of a 14 m hill.
16. What is the potential energy of a rock that is resting on the edge of a cliff 17 meters above the ground, if the mass of the rock is 58 kg?
PE = mgh
17. What is the kinetic energy of a truck if the mass of the truck is 14,786 kg and has a velocity of 12 m/s? KE =.5 mv2 KE = .5 x mass x velocity squared
18. What happens to the kinetic and potential energy of a 5.0 kgrock that falls from 9.0 meters? Remember that starting potential energy equals the ending kinetic energy because energy is conserved. Label the amount of energy for every 3.0 m fallen.
Height(m) / Potential Energy
(J) / Kinetic Energy
(J)
KE =.5 mv2 / Total Energy
(J)
9 m / mgh = 5 x 9.8 x 9 / 0 (It’s not moving yet) / Same as PE
6 m / mgh: here h= 6 / Total E – PE left / Same every time:
3 m / Total E – PE left / Energy is conserved.
0 m / All the PE is now KE.
19. Aconstruction workerwith aweight of 1269 N is standing on top of a 6.0m high ladder. What is the Potential and Kinetic Energy of the construction worker on top of the ladder?
20. The Construction worker from the previous problemfalls off the ladder andhitsthe ground.What is the PE and Kinetic Energy of the construction workerjust before hitting the ground? What is the construction worker's velocity when about to hit the ground?
PELost = KEGainedmghtop = .5mv2 Lower Last step: Solve for v
21. After finishing her physics homework, Marissa pulls her 55 kg body out of the living room chair and slowly climbs up the 3.5 m high flight of stairs to her bedroom. How much work does Marissa do in ascending the stairs?
22. In the previous problem, Marissa slowly ascended the stairs, taking 11 seconds to go from the bottom to the top. The next evening, in a rush to catch a phone call from her boyfriend, she runs up the stairs in 4.0 seconds. On which night does Marissa do more work? On which night did Marissa generate more power? What is the difference in power?
23. What is the power of an engine, if it can propel a 13 kg toy car a distance of 5.0 m in 3.0 seconds? The acceleration of that car is 4.0m/s2
24. If a boat motor produced2,858 kW of power while moving its3,333 kg boat a distance of 300 m in 5.0 seconds, what would the acceleration of the boat be?
25. An object is being lifted up. Is the GPEincreasing or decreasing?
26. A rock is falling down. As it is falling, what happens to(a) its GPE? (b) It’s KE?
27. Joshua, a SanFrancisco hot dog vender, has fallen asleep on the job. When an earthquake strikes, his cart rolls down Nob Hill and reaches point A ata speed of 2.0 m/s. How fast is the hotdog cart going at point B when Joshua catches up to it?
28. A hippo starts from rest at the top of a 65 m hill, skis down a 40 degree incline into a valley and continues up the a 47 m hill. Both hill heights are measured from the valley floor. Neglect the effects of friction.(a) How fast is the hippo moving at the bottom of the valley?(b) What is the hippo's speed at the top of the next hill?