A billiard ball of mass .155 kg moves with a velocity of 12.5 m/s toward a stationary billiard ball of identical mass and strikes it in a head on collision. The first billiard ball comes to a complete stop. Was the collision elastic?

1 Answer
Mar 18, 2018

Suppose,a ball of mass mm moving with velocity vv collided with a mass of mm at rest and the first mass came to rest.

Let,after the collision velocity of the 2nd mass will be v'

So,applying law of conservation of momentum,

mv+0=0+mv'

so,v'=v

so,kinetic energy before the collision =1/2 mv^2 +0=1/2mv^2

and after the collision,kinetic energy became =0 +1/2 mv'^2 =1/2 mv^2

So,kinetic energy before and after the collision remains the same.

Hence it was an elastic collsion.

Remember,in an elastic collsion,two identical mass just exchange their velocity.

And,coefficient of restitution is 1