A man of mass m is standing on a platform of mass M kept on smooth ice. If the man starts moving on the platform with a speed v relative to the platform with what velocity relative to the ice does the platform recoil?

Explanation

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_(2)v rArr v=(m_(1)v_(r))/(m_(1) + m_(2)`