A $$1 \mathrm{~kg}$$ ball moving at $$12 \mathrm{~ms}^{-1}$$ collides with a $$2 \mathrm{~kg}$$ ball moving in opposite direction at $$24 \mathrm{~ms}^{-1}$$. If the coefficient of restitution is $$2 / 3$$, then their velocities after the collision are

A ball hits the floor and rebounds after an inelastic collision. In this case

During inelastic collision between two objects, which of the following quantity always remains conserved?

Two particles which are initially at rest move towards each other under the action of their mutual attraction. If their speeds are $$v$$ and $$2 v$$ at any instant, then the speed of centre of mass of the system is