If a pendulum is oscillating with a frequency f then what is the frequency at which it's K.E. changes?
Correct answer: A. 2f
- A. 2f
- B. f/2
- C. F
- D. None of these
Explanation
In a simple pendulum, the potential energy is maximum when the displacement is maximum, and the kinetic energy is maximum when the velocity is maximum. At the mean position, the displacement is zero, and the velocity is maximum. Thus, the kinetic energy is maximum at the mean position. The pendulum passes through the mean position twice in each complete oscillation cycle, once while moving from left to right and once while moving from right to left. Therefore, the frequency at which the kinetic energy changes is twice the frequency of oscillation, which is given by 2f.
This question appeared on the NUMS 2019 (cancelled sitting) paper, which you can sit online with every answer explained.
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About Simple Harmonic Motion
Simple harmonic motion is oscillation in which acceleration is directly proportional to displacement and directed toward the equilibrium position. Work includes displacement, velocity, acceleration, phase, period, frequency, amplitude and energy, with applications to springs and simple pendulums. The restoring force and the conditions for SHM distinguish it from general periodic motion.
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