# Math Help - Find energy

1. ## Find energy

Two balls with masses of 2.0 kg and 6.0 kg travel towards each other at speeds of 12 m/s and 4 m/s. If the balls have a head on, inelastic collision and the 2.0 kg ball recoils with a speed of 8.0 m/s, how much kinetic energy is lost in the collision?

2. Originally Posted by John 5
Two balls with masses of 2.0 kg and 6.0 kg travel towards each other at speeds of 12 m/s and 4 m/s. If the balls have a head on, inelastic collision and the 2.0 kg ball recoils with a speed of 8.0 m/s, how much kinetic energy is lost in the collision?
It depends on how fast the 6.0 kg ball is traveling after the collision.

All we can say is that the initial total kinetic energy is
$K_{tot} = \frac{1}{2}(2.0)(12)^2 + \frac{1}{2}(6.0)(4)^2 = 192~J$

and that after the collision the 2.0 kg ball is carrying
$K_{2.0} = \frac{1}{2}(2.0)(8.0)^2 = 64~J$

but we have no information on how much KE the other ball has after the collision.

-Dan