Question

A ball with a mass of `15 kg` moving at `15 m/s` hits a still ball with a mass of `17 kg`. If the first ball stops moving, how fast is the second ball moving? How much kinetic energy was lost as heat in the collision?

Answer 1

well as no external force is acting during this motion and collision,we can say,the linear momentum of the system will be conserved.

So,let the 2nd ball will move with a velocity of `v` after the collision.

So,momentum before the collision is `(15*15 +17*0) Kgms^-1` (considering the `2` nd ball was at rest before the collision)

And,momentum after the collision will be `(15*0 + 17*v) Kgms^-1`

So,we can equate both,

`15*15 = 17*v`

So, `v=13.234 ms^-1`

so,initial kinetic energy of the system was, `K.E _(i)=1/2 15 *15^2 J`(using, `K.E. =1/2 mv^2`)

And,after the collsion it became `K.E_(f)=1/2 17 (13.234)^2 J`

So,energy lost is `K.E_(f) - K.E(i) =198.81 J`