Download Phys 30 Mech Exam 2010

Mechanical Energy Exam
Please circle the correct or best answer (1 mark each)
1. The losing team in a tug-of-war would be an example of
a) positive work
b) negative work
c) positive force
d) negative force
2. Which of the following can be found by calculating the area under an applied force verses
displacement graph
a) time
b) work
c) force
d) power
3. The rate at which work is done is called
a) time
c) power
b) force
d) energy
4. Both momentum and kinetic energy are conserved in
a) a glancing collision
b) an elastic collision
c) an inelastic collision
d) a conservation collision
5. A pendulum would have the greatest amount of kinetic energy when
a) at the top of its swing
b) at the bottom of its swing
c) it is swinging upwards
d) it is swinging downwards
6. When an object is at rest, which of the following may it have?
a) kinetic energy
b) potential energy
c) both kinetic and potential energy
d) neither kinetic or potential energy
7. How much work is done on a 50 N rock when it is raised 2 m?
a) 25 J
b) 75 J
c) 100 J
d) 200 J
8. A 10.0 kg object is accelerated horizontally from rest to a velocity of 11.0m/s in 5.0s by a
horizontal force. How much work is done on this object assuming the object is on a
frictionless surface?
a) 220 J
b) 550 J
c) 605 J
d) 725 J
9. A 45.0 kg student runs at a constant velocity 9.0 m up an incline that is 6.0 m tall. If the
power output of the student is 1500 W, how long does it take the student to run the 9.0 m up
the incline?
a) 1.8 s
b) 2.6 s
c) 2600 s
d) 4000 s
10. Claire drops an object from the top of a building and hits the ground with a speed of 13m/s.
From what height was it dropped
a) 8.6m
b) 17.2m
c) 127.4m
d) 213.2m
11. A 20 kg object is dropped by Miriah from the top of a 72m cliff. What is its kinetic energy as
it hits the ground?
a) 38 J
b) 1.4 10 3 J
c) 1.4 10 4 J
d) 2.8 104 J
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II. Short Answer - Please show all of your work.
13. Aaron pushes horizontally with a 80 N force on a 20 kg mass 10 m across a floor.
Calculate the amount of work Aaron did. (2 marks).
14. Michelle pulls a 90.0 N box 10.0 m along a level surface by a rope. If the rope makes an
angle of 20 with the surface, and the force exerted through the rope is 75.0 N, how
much work is done on the box? (3 marks)
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15. Kim, a champion weightlifter, raises 240 kg a distance of 2.35 m (6 marks).
a) How much work is done by Kim lifting the weights?
b) How much work is done holding the weights above her head?
c) How much work is done lowering them back to the ground?
d) Does Kim do work if the weights are let go and fall back to the ground?
e) If Kim completes the lift in 2.5 s, how much power is developed?
16. An 845 N sled is pulled by Kaitlyn a distance of 185 m. The task requires 1.2 10 4 J of
work and is done by pulling on a rope with a force of 125 N. At what angle is the rope
held (with respect to the ground)? (3 marks)
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17. Katie hoists a 98 N sack of grain to a storage room 50 m above the ground floor of a
grain elevator (5 marks).
a) How much work was required to lift the sack of grain?
b) What is the potential energy of the sack of grain at this height?
c) The rope being used to lift the sack of grain breaks just as the sack reaches the storage
room. What velocity does the sack have just before it strikes the ground floor?
18. A racing car has a mass of 1500 kg. What is its kinetic energy if it has a speed of 108
km/h? (3 marks)
19. Bryce raised a 12.0 N physics book from a table 75 cm above the floor to a shelf, 2.15 m
above the floor. What was the change in potential energy? (3 marks).
20. Amanda drops a watermelon from a building. It has a kinetic energy of 400J and a
velocity of 18m/s when it hits the ground. From what height was the watermelon
dropped? (3 marks)
21. A 2.0 kg rock initially at rest loses 400 J of potential energy while falling to the ground
(4 marks).
a) Calculate the kinetic energy that the rock gains while falling.
b) What is the rock’s speed just before it strikes the ground?
22. A physics book, mass unknown, is dropped 4.50 m. What speed does the book have just
before it hits the ground? (3 marks)
23. From what height would Don’s compact car have to be dropped to have the same kinetic
energy that it has when being driven at 28 m/s? (3 marks)