Question

A light rigid rod of length $L=\frac{8}{5}$ m hinged at one end has a bob of mass m attached to its other end. Find speed (in m/s) of bob at the lowest point when rod is released from vertical position.

Answer 1

Initial energy ( keeping lowest point as reference) $=2Lmg$
Final energy $=\frac{1}{2}m{v}^2$
Conserving the energy: $\frac{1}{2}m{v}^2=2Lmg$
$v^2=4Lg\Rightarrow v=2\sqrt{Lg}=2\sqrt{\frac{8}{5}\times 10}=2\times 4=8m/s$