Work

1)         Energy is required to cause change. As our solar system was being formed, the temperature at the center of the gas cloud changed so dramatically that the hydrogen began to fuse. That means a lot of work was done. What did all the work on the little molecules?

2)         Can work be done on an object that remains at rest? Please explain.

3)         Chemical reactions (burning things, for example) can release considerable potential energy, which can then be used to do work. But potential energy is caused by force. What is the force that causes the so-called “chemical” potential energy?

4)         Activation energy is needed to start a chemical reaction. This is another way of saying that work must be done on the chemicals involved before they will react. Describe the work being done at the atomic level.

5)         A moving car has kinetic energy. Work must be done to make the car stop moving. What is the force that does the work, and what is the distance over which the force acts? Assume the tires do not slide across the pavement.

6)         A tow rope, oriented parallel to the water, pulls a waterskier for a distance of 86 m. The work done on the skier is 1.9 × 10 4 J. First, calculate the tension in the tow rope. Second, since work was done on the skier, which required energy, and energy must be conserved, where is the energy now?

7)         Your friend moves into an apartment at the beginning of a college semester. His weight is 685 N. (Is that a lot?) His belongings weigh 915 N. How much work does the elevator do while lifting your friend and his belongings 15.2 m upwards at a constant velocity? How much work does the elevator do on your friend  without his belongings – on the downward trip, also at a constant velocity?

8)         A person pulls a toboggan at a constant velocity for a distance of 15.0 m by pulling on a rope that makes an angle of 25.0° above the snow. If the tension in the rope is 94.0 N, how much work is done by friction?

9)         Now slide the toboggan down a hill. The height of the hill is 13 m and the distance the toboggan slides is 35 m. The mass of the toboggan and passengers is 140 kg and the angle of the hill is 22°. How much work is done by gravity?

10)       You pull a sofa 1.5 m across a carpeted floor using a 210 N force, 40.0° above the horizontal. The mass of the sofa is 35 kg. If the kinetic frictional coefficient (mk) is 0.32 what is the net work done on the sofa? (Remember, the normal force is not mg.)