Question

A rod of mass $m$ and length $l$ is lying on a horizontal table. Work done in making it stand on one end will be

Answer 1

Work done = Change in the potential energy

The center of mass of the rod is at its midpoint.When the rod is in the horizontal position its potential energy is zero.

When the rod is in the vertical direction, i.e. stands on one of its end the center of mass is at the point, $h=\frac{l}{2}$

→Work done $=mgh=mg\left(\frac{l}{2}\right)$

or Work done$=\frac{mgl}{2}$