A man of mass m moves with a constant speed on a plank of mass M and length L kept initially at rest on a frictionless horizontal surface . From one end to the other he reaches in time t . The speed of the plank relative to ground while man is moving , is

Options

A. `l/t(M/m)`
B. `l/t(m/(m+M))`
C. `l/t(M/(M +m))`
D. None of these

Answer

B

Explanation

`v_(r) = l/t`, Now , `m(v_(r)-v) = Mv` (v= speed of plank)
`v=(mv_(r)/(M +m)` = l/t(m/(M +m)`