## The balls, having linear momenta $p _{1}=pi^$ and $p _{2}=−pi^$, undergo a collision in free space. There is no extemal force acting on the balls. Let $p _{1}$ and $p _{2}$ be their final momenta. The following option(s) is (are) NOT ALLOWED for any non-zero value of $p,a_{1},a_{2},b_{1},b_{2},c_{1}$ and $c_{2}$.