Question

A man of 30 kg walking on a plank of 100kg find the displacement of plank?

Answer 1

Let plank is large enough. Since external force acting on the plank is zero hence center of mass of the system will remain same.

If d is distance travelled by man and x is distance travelled by plank then in center of mass frame,

$30 d = (30 + 100)(x)$

$x = \frac{30}{130} d = \frac{3}{13}d$