A flat car of mass `m` is at rest on a frictionless floor with a child of mass `m` standing at its edge. If the child jumps off from the car towards right with an initial velocity `u`, with respect to the car, find the velocity of the car after its jump.

Explanation

Let car attains a velocity v, and the net velocity of the child with respect to earth will be u – v, as u is its velocity with respect to car.

Initially, the system was at rest, thus according to momentum conservation, momentum after jump must be zero, as
`m(u-v)=Mv`
`v=(mu)/(m+M)`