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Chapter 9: Q. 2 (page 227)
At what speed does a 1000 kg compact car have the same kinetic energy as a 20,000 kg truck going 25 km/h?
The speed should be 11.8 km/hr.
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The driver of a car traveling at 60 mph slams on the brakes, and the car skids to a halt. What happened to the kinetic energy the car had just before stopping?
You need to raise a heavy block by pulling it with a massless rope. You can either (a) pull the block straight up height h, or (b) pull it up a long, frictionless plane inclined at a 15 o angle until its height has increased by h. Assume you will move the block at constant speed either way. Will you do more work in case a or case b? Or is the work the same in both cases? Explain.
A mother has four times the mass of her young son. Both are running with the same kinetic energy. What is the ratio vson /vmother of their speeds?
A kg sprinter, starting from rest, runs m in s at constant acceleration.
a. What is the magnitude of the horizontal force acting on the sprinter?
b. What is the sprinter’s power output at s, s, and s?
a. How much work does an elevator motor do to lift a kg elevator a height of m?
b. How much power must the motor supply to do this in s at constant speed?
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