question_answer

The time period of a simple pendulum in a lift descending with constant acceleration \[g\] is:

A) \[T=2\pi \sqrt{\frac{l}{8}}\]                         

B)  \[T=2\pi \sqrt{\frac{l}{2g}}\]

C)   zero                                    

D)   infinite

Correct Answer: D

Solution :

Key Idea: When lift is descending effective acceleration decreases. The time period of a simple pendulum in descending lift is given by Effective acceleration when lift is descending is given by                 \[Tmg-T=mg\] or            \[T=0\] or            \[mg'=0\] or            \[g'=0\] Hence,  \[T=2\pi \sqrt{\frac{l}{0}}=\infty \]