Question

A man of mass M stands at one end of a stationary plank of length L, lying on a smooth surface. The man walks to the other end of the plank. If the mass of the plank is `M//3`, the distance that the man moves relative to the ground is
A. `(3L)/4`
B. `L/4`
C. `(4L)/5`
D. `L/3`

Answer 1

Correct Answer - B
Let plank moves x distance in opposite direction. Then, displacement of man relative to ground will be, (L-x), Applying
`m_(B)x_(B) = m_(L)x_(L)` or `M(L-x) =M/3x`
Solving the equation we get, `x = (3L)4`
`therefore` Displacement of man relative to ground = L - (3L)/4 = L/4`