A body of mass $2m$ hits a rigid wall normally with velocity $3v$ and bounces back with the same spe

Question

A body of mass $2m$ hits a rigid wall normally with velocity $3v$ and bounces back with the same speed. The impulse experienced by the body is

Professor PC Thomas Classes · Answer

Initial momentum $p_i = (2m)(3v) = 6mv$ (towards wall). Final momentum $p_f = -(2m)(3v) = -6mv$ (away from wall). Impulse = change in momentum = $p_f - p_i = -6mv - 6mv = -12mv$. The magnitude of the impulse is $12mv$.