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

Since there is no external force acting on the system, the linear momentum of the system must be conserved. Hence momentum before collision = momentum after collision
→mv + 0 = 0 + (2m)v'
v' = v/2
The coefficient of restitution = Velocity of separation / Velocity of approach
= v' / v = 1/2 = 0.5