In Example 9.6 (p. 217), of the skier is gliding down the slope at a constant speed, how much work would be done by friction on the skier?

As a pendulum bob swings back and forth several times, the maximum height it reaches becomes less and less. this is because more and more of the pendulum bob's energy is being transformed into a. heat energy b. kinetic energy c. potential energy d. kinetic energy and potential energy