Question

A ball with a mass of `5 kg` is rolling at `3 m/s` and elastically collides with a resting ball with a mass of `2 kg`. What are the post-collision velocities of the balls?

Answer 1

`v_1=9/7 m/s`
`v_2=30/7 m/s`

Explanation:

`5*3+0=5*v_1+2*v_2`
`15=5*v_1+2*v_2" (1)"`
`3+v_1=0+v_2" (2)"`
`color(red)"'the sum of the velocities of objects before and after collision must be equal'"`
`"write " v_2=3+v_1" at (1)"`
`15=5*v_1+2*(3+v_1)`
`15=5.v_1+6+2*v_1`
`15-6=7*v_1`
`9=7*v_1`
`v_1=9/7 m/s`
`use :" (2)"`
`3+9/7=v_2`
`v_2=30/7 m/s`