For a simple pendulum, having time period T, the variation of kinetic energy (K.E.) with time (t) is represented by :
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Answer
(4) [figure]
Solution
Take the bob released from an extreme position: x = A t ⇒ v = -A t
⇒ K.E. = 12mv2 = 12m 2A2 2 t
∴ K.E. is never negative, so it cannot be constant or go below zero.
K.E. = 0 at t = 0, T2, T (extreme positions) and maximum at T4, 3T4 (mean position).
∴ K.E. varies periodically with period T2, as two humps in one time period, touching the t-axis at 0, T2 and T: graph (4).
Answer: (4)