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Physics 11 Assignment
Chapters 6 & 7 - Work, Energy & Power
1. Define the following terms:
 Kinetic energy
 Gravitational potential energy
 Elastic potential energy
 Mechanical energy
 Conservative force
 Non-conservative force
 Work
 Joule
 Work-kinetic energy theorem
 Law of conservation of energy
 Hooke’s law
 Restoring force
 Spring constant
 Power
 Efficiency
2. Can the normal force on an object ever do work? Explain.
3. A woman swimming upstream is not moving with respect to the shore. Is she doing any work? If she stops
swimming and merely floats, is work done on her?
4. Why is it tiring to push hard against a solid wall even though no work in done?
5. By approximately how much does your gravitational potential energy change when you jump as high as you
can?
6. A pendulum is launched from a point that is a height h above its lowest
point in two different ways (see figure to the right). During both launches,
the bob is given an initial speed of 3.0 m/s. On the first launch, the initial
velocity of the bob is directed upward along the trajectory, and on the
second launch, it is directed downward along the trajectory. Which launch
will cause the pendulum to swing the largest angle for the equilibrium
position?
7. A coil spring of mass m rests upright on a table. If you compress the
spring by pressing down with your hand and then release it, can the spring
actually leave the table? Explain using the law of conservation of energy.
8. Analyze the motion of a simple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking
it into account. Explain why a grandfather clock has to be wound up.
9. Suppose you lift a suitcase from the floor to a table. Does the work you do on the suitcase depend on (a)
whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the
table, and (d) the weight of the suitcase?
10. Answer the previous question for the power needed rather than the work.
11. A 75.0-kg firefighter climbs a flight of stairs 10.0 m high. How much work in required?
12. A 9.0 x 102-N crate rests on the floor. How much work is required to move it at constant speed (a) 6.0 m
along the floor against a friction force of 180 N, and (b) 6.0 m vertically.
13. How much work did the movers do (horizontally) pushing a 150-kg crate 12.3 m across a rough floor
without acceleration, if the effective coefficient of friction was 0.70?
14. The horizontal x component of the force on an object varies as shown in the graph below. Determine the
work done by this force to move the object (a) from x = 0.0 m to x = 10.0 m, and (b) from x = 0.0 m to x =
15.0 m.
15. A spring has a spring constant of k = 88 N/m. Determine the work needed to stretch it from x = 3.8 cm to x
= 5.8 cm, where x is the displacement from its unstretched length.
16. How much work is required to stop an electron (m = 9.11 x 10-31 kg) which is moving with a speed of 1.90 x
106 m/s?
17. A spring has a spring constant k = 440 N/m. How much must this spring be stretched to store 25 J of elastic
potential energy?
18. A roller coaster, as shown below, is pulled to a point 1 where it is released from rest. Assuming no friction,
calculate the speeds at points 2, 3 & 4.
19. How long will it take a 1750-W motor to lift a 285-kg piano to a sixth-story window 16.0 m above?
20. An engine produces 8200 J of heat while performing 3200 J of useful work. What is the efficiency of this
engine?