A sphere of mass $m_1= 2 kg$ collides with a sphere of mass $m_2= 3 kg$ which is at rest. Mass $m_1$will move at right angles to the line joining the centres at the time of collision,the coefficient of restitution is

Question

$$\begin {array} {1 1} (a)\;\frac{4}{9} & \quad (b)\;\frac{1}{2} \\ (c)\;\frac{2}{3} & \quad  (d)\;\sqrt {\frac{2}{3}} \end {array}$$