Elastic collision and energy conservation

2026 Re-NEET 1 question

1. Bob B of mass m at rest is hanging vertically from the ceiling via a massless string of length 10 m, as shown in the figure. Point mass A of mass m travelling horizontally with speed 10 ms$^{-1}$ hits bob B elastically. The bob B rises h meter after the collision. Taking the acceleration due to gravity g = 10 ms$^{-2}$ and neglecting the size of the bob, the value of h is: