Question

A man of mass $m$ standing on a plank of mass $M$ which is placed on a smooth horizontal surface, is initially at rest. The man suddenly starts running on the plank with a speed of $vm/s$ with respect to the ground. Find the speed of the plank with respect to the ground

Answer 1

Given,

From conservation of momentum

Final momentum = initial momentum

$MV+mu=0$

$u=\frac{-Mv}{m}$

Velocity of plank is $\frac{-Mv}{m}$ , negative sign mean, direction of motion is opposite.