A block having mass m collides with an another stationary block having mass 2 m. The lighter block comes to rest after collision. If the velocity of first block is v, then the value of coefficient of restitution will must be [AIIMS 2015]

Let the velocity of block of mass 2 m after the collision be v', then from law of conservation of momentum,                     mv=2mv'⇒v'=v2Now, the coefficient of restitution,                      e=velocity of separationvelocity of approach= v'v=v/2v=12=0.5