Question

A child swinging on a swing $m$ a sitting position, stands up, then the time period of the swing will:

• A. increase
• B. decrease
• C. remain same
• D. increase if the child is long and decrease if the child is short

Answer 1

Answer: (B)

When child stands up centre of mass shifts upwards.
The child swings in simple harmonic motion,
hence time-period is given by
$T=2\pi \sqrt{\frac{l}{g}}$
$\Rightarrow T\propto \sqrt{l}$
where $l$ is length of swing.
When child stands up,
the length is shortened as centre of mass shifts up,
hence time period decreases.