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A flat car of mass m is at rest on a fri...

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.

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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=(m u)/(m+M)`.
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