Q102 / 180 · AIIMS 2018 (27 May) · Physics

Assertion : If a pendulum is suspended in a lift and lift is falling freely, then its time period becomes infinite. Reason : Free falling body has acceleration equal to acceleration due to gravity.

  • A
    If both assertion and reason are true and reason is the correct explanation of assertion.
  • Correct answer
    B
    If both assertion and reason are true but reason is not the correct explanation of assertion.
  • C
    If assertion is true but reason is false.
  • D
    If both assertion and reason are false.

Solution

If a pendulum is suspended in a lift and lift is moving downward with some acceleration $a$, then time period of pendulum is given by, $T=2 \pi \sqrt{\frac{l}{g-a}}$ In the case of free fall, $a=g$ then $T=\infty$ i.e., the time period of pendulum becomes infinite.

Hence, the correct answer is option: 'B'.

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