A 2.50-kg rock is attached at the end of a thin, very light rope 1.45 m long. You start it swinging by releasing it when the rope makes an 11° angle with the vertical. You record the observation that it rises only to an angle of 4.5° with the vertical after swings.

(a) How much energy has this system lost during that time?

(b) What happened to the “lost” energy? Explain how it could have been “lost.”