question_answer 43)

                  Which of the diagrams shown in Fig. represents variation of total mechanical energy of a pendulum oscillating in air as function of time?                 (a)       (b)                 (c)        (d)                

Answer:

                  (a) When pendulum oscillates in air, total mechanical energy (K.E. + P.E.) decreases with time because a part of mechanical energy is used to overcome the force of friction offered by air.