Question

A man of mass `m_1` is standing on a platform of mass `m_2` kept on a smooth horizontal surface. The man starts moving on the platform with a velocity `v_r` relative to the platform. Find the recoil velocity of platform.

Answer 1

Correct Answer - A::B
Absolute velocity of man `=v_r-v` where v=recoil velocity of platform.

Taking the platform and the man as a system, net external force on the system in horizontal direction is zero. The linear momentum of the system remains constant. Initially both the man and the platform were at rest.
Hence, `0=m_1(v_r-v)-m_2v`
`:. v=(m_1v_r)/(m_1+m_2)`
Alternate Method Using the equation,
`summ_Rv_R=summ_Lv_L`
we have, `m_1(v_r-v)=m_2v`
`:. v=(m_1v_r)/(m_1+m_2)`