Question

A simple pendulum is attached to the roof of a lift. Its time period of oscillation, when the lift is stationary is 0.5 s. Its frequency of oscillation when the lift falls freely will be

• A. infinite
• B. zero
• C. 2 Hz
• D. 20 Hz

Answer 1

The correct option is B zero

When lift falls with acceleration g, net effective force acting on pendulum is 0 (mg downwards due to gravity and mg upwards due to pseudo force.). Thus net acceleration will be zero.
Now, frequency, $f=1/T=1/2\pi \sqrt{g_{eff}/l}=0$ (because $g_{eff}=0$)