Q94
General SciencePhysics
A person on a swing stands up. The time period of the swing
- a.increases
- b.remains the same
- c.decreases
- d.becomes zero
Answer: (C) decreases
A swing behaves like a pendulum with $T=2\pi\sqrt{\frac{L}{g}}$, where $L$ is the distance from the point of suspension to the centre of mass. When the person stands up, the centre of mass rises, the effective length decreases, and so the time period decreases (the swing oscillates faster). $T$ does not depend on mass, so a second person merely sitting alongside makes no difference. Reverse cases: $T$ increases on the Moon or on a mountain (smaller $g$) and becomes infinite in a freely falling lift or an orbiting satellite.