Question

A ball of mass 5 kg with velocity 3m/s strikes a ball of mass 2 kg kept at rest. If the lighter ball moves with a velocity 2m/s after the collision find the velocity of the heavier object?

Answer 1

We use conservation of kinetic energy as we cannot use conservation of linear momentum as direction of the ball after collision is not known

KE before collision =12=12m.102+0m.102+0

=50mJ=50mJ

KE after collision =12=12m×82+12m×82+12mv2mv2

=(32+12=(32+12mv2)Jmv2)J

32m+1232m+12mv2=50mmv2=50m

v2=36v2=36

v=6v=6m/sm/s

Since we see that 102=82+62102=82+62

The two balls must be moving at right angles to each other.