Question

A ball with a mass of `3 kg` is rolling at `15 m/s` and elastically collides with a resting ball with a mass of `4 kg`. What are the post-collision velocities of the balls?

Answer 1

`v_1=-15/7 m/2`
`v_2=90/7`m/s

Explanation:

`"we must use conservation of momentum to solve this problem."`
`vec P_1+ vec P_2=vec P_1^'+vec P_2^'`
`3*15 +0=3*v_1+4*v_2`
`15+v_1=0+v_2`
`v_1=v_2-15`
`3.15=3(v_2-15)+4*v_2`
`45=3*v_2-45+4*v_2`
`90=7*v_2`
`v_2=90/7`m/s
`v_1=90/7-15`
`v_1=-15/7 m/2`