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Kreutter: Work and Energy
Name:_________________________
Date:_____________
Period:________
Work and Energy Problem-Solving Study Guide
1. Albert, all 75-kg of him, is skiing. Initially, he is at the top of a frictionless hill that is 45
meters high. His final situation is moving very fast at the bottom of the hill.
a. Draw an energy bar chart that represents this process if we consider the system to
be only Albert.
b. Draw an energy bar chart that represents this process if we consider the system to
be Albert and the Earth.
c. What if the hill is not frictionless? How would this change the bar charts you drew in
a and b?
d. How fast is Albert going at the bottom of the hill?
2. Isaac exerts a constant force of 8.3-N on a hockey puck that is sliding across a frozen
pond. If he exerts the force over 0.25 meters, how much work does Isaac do on the puck?
What is the change in the puck’s energy? Draw an energy bar chart to represent this
process. What is your system? Write an equation that also represents the situation.
Kreutter: Work and Energy
Name:_________________________
Date:_____________
Period:________
3. What if the force Isaac exerts is opposite the direction of the puck’s motion? How much
work does he do? What is the change in the puck’s energy?
4. Does the work required to lift a book to a high shelf depend upon how fast you raise it?
Does the power required to lift a book depend upon how fast you raise it? Explain.
5. Isaac, Albert, Enrico, Nikola, Thomas, and Marie are riding an elevator. Their combined
mass is 385-kg, and their trip is from the first to the third floors, a distance of 45.0
meters. It takes 20 seconds. How much power does the elevator generate?
6. Isaac built a go-cart and is testing it. Together, Isaac and his go-cart have a mass of 140kg. If, at the bottom of a hill, Isaac and his go-cart have 1.7x 103 J of kinetic energy, what
was the height of the hill Isaac traveled down?
Kreutter: Work and Energy
Name:_________________________
Date:_____________
Period:________
7. Remember our stomp rockets. The mass of a stomp rocket is 200-g and the maximum
height reached is 275 meters.
a. Draw an energy bar chart that shows the rocket’s initial situation right after it’s
launched and its final situation as being this maximum height. What is your system?
b. Now draw an energy bar chart using the rocket at its maximum height as the initial
situation and right before it hits the ground as the final state. Write an equation that
represents what the bar chart shows.
c. What is the velocity of the rocket right before it hits the ground?
8. If the work done on an object doubles its kinetic energy, does it double its velocity? If
not, by what ratio does it change the velocity?
Kreutter: Work and Energy
Name:_________________________
Date:_____________
Period:________
9. Nikola pushes a heavy box across the floor with a force of 70 Newtons with a constant
speed of 0.40 m/s. What is the net work done on the box? How much work does Nikola
do on the box?
10. Albert lifts a 20.0-kg block to a height of 2.0 m in 5.0 s. Marie lifts 30.0 kg to a height of
1.5 m in 8.0 s. How much work does each person do? How much power does each
person generate?
11. During a tug-of-war, Team Nikola does 3.7 x 105 J of work pulling Team Thomas 10.0
meters. What force was Team Nikola exerting?
12. Enrico exerts a force of 25.0 N as he rides a bike 375 m in 42.0 s. How much power does
he develop?
13. Thomas is lifting weights. He can raise 100-kg of weights a distance of 1.8 meters,
which is straight over his head.
a. How much work does Thomas do when he is lifting the weights over that distance?
Kreutter: Work and Energy
Name:_________________________
Date:_____________
Period:________
b. How much work does he do if he holds the weights over his head for 10 seconds?
c. How much work does he do if he lowers the weights back down to the ground?
d. Does Thomas do work if he lets go of the weights and they fall back down to the
ground?
e. If Thomas lifts the weights in 2.7 seconds, how much power does he develop?
14. Albert and Isaac are moving 90-N cartons of books from the floor to a platform Albert
moves 11 cartons in 6 minutes while Isaac moves 11 cartons in 5 minutes. Who does
more work? Explain your answer.
15. Albert and Isaac exert a total force of 890 N in moving a heavy sofa 14 m to another
room. Isaac exerts twice as much force as Albert. How much work does each person do?
Kreutter: Work and Energy
Name:_________________________
Date:_____________
Period:________
16. Nikola lifts a 7.5-kg spool of copper wire from the floor to a height of 0.70 m, carries it
45 m at constant speed across his laboratory and then places it on a shelf 1.5 m above
the floor. How much work does he do?
17. At what speed can a 120-W motor lift a 2800-N load?
18. You are designing a skateboard park. The starting ramp is supposed to be 0.61 m high.
a. What would be the potential energy of a 63.5-kg skateboarder at the top of the
starting ramp?
b. How could you change the ramp design so that a 63.5-kg skateboarder moves twice
as fast at the bottom? Ignore air resistance and friction between the skateboard
and the ramp. Why would this design change work in terms of conservation of
energy?
c. Assume that the same 63.5-kg skateboarder in part B falls off the side of the ramp.
What is the kinetic energy of the skateboarder on the ground at the bottom of the
ramp?
Kreutter: Work and Energy
Name:_________________________
Date:_____________
Period:________
19. What is the gravitational potential energy of a passenger jet weighing 7.5 x 105N when
it reaches a cruising altitude of 10 km?
20. How many joules of work were done to lift the plane in the last question to that altitude?
21. How much work must be done to stop a steel ball with a mass of 4.0 kg rolling across a
frictionless surface at a speed of 62 m/s?
22. What is the relationship between momentum and kinetic energy? Explain how
momentum can be conserved in a collision where kinetic energy is not conserved.
23. An archer fires a 0.30-kg arrow from a bow. The archer exerts an average force of 200 N
to draw the string back 1.3 m.
a. Assuming no friction, at what speed does the arrow leave the bow?
b. If the arrow is shot straight up, what height does it reach?
24. Which has the greater gravitational potential energy—a 550-g flowerpot sitting on a
1.2-m high shelf or a 350-g flowerpot sitting on a 1.8-m high shelf?
Kreutter: Work and Energy
Name:_________________________
Date:_____________
Period:________
25. Under what conditions will a moving 0.030kg marble and a moving 3.00kg rock have
the same kinetic energy?
26. Albert is throwing bowling balls. If he throws a 7.0kg ball straight up in the air, exerting
a force of 810 N on the ball over a distance of 2.0m, how high did the ball go from the
point of release?
27. Why must the first hill of a roller coaster be the highest?
28. What is the orbital speed of a satellite orbiting 350 km above the surface of the Earth?
Use massEarth = 5.98 x 1024 kg and a radius of 6.38 x 106m.
29. The Sun has a mass of 1.99 x 1030 kg. The planet Neptune has a mass of 1.03 x 1026 kg
and is 4.50 x 1012 m from the Sun. Calculate the gravitational force between the Sun
and Neptune.