# Two particles approach each other with different velocities. After collision , one of the particles has a momentum $\overrightarrow {p}$ in their center of mass frame. In the same frame, the momentum of the other particle is

$\begin {array} {1 1} (a)\;0 & \quad (b)\;-\overrightarrow{p} \\ (c)\;-\overrightarrow {p}/2 & \quad (d)\;\overrightarrow{p}\end {array}$

Centre of mass frame is a zero momentum frame.