Three objects `A, B` and `C` are kept in a straight line on a frictionless horizontal surface. These have masses `m, 2m` and `m`, respectively. The object `A` moves towards `B` with a speed `9 m//s` and makes an elastic collision with it. Thereafter, `B` makes completely inelastic collision with `C`. All motions occur on the same straight line. Find the final speed (in `m//s`) of object `C`.

Answer

`4 m//s`

Explanation

For collision between A & B
`v_(A) = ((m - 2m))/((m + 2m)) (9) = -3 ms^(-1)`
`v_(B) = (2(m))/((m + 2m))(9) = +6ms^(-1)`
For collision between B and C
`v_(c ) = ((2m)/(2m + m)) (6) = 4ms^(-1)`