A rifle of mass `M` is initially at rest but free to recoil. It fires a bullet of mass `m` and velocity `v` (relative to the ground). After firing, the velocity of the rifle (relative to the ground) is _______?

Answer

`-mv//M`

Explanation

conservation of momentum
`Mv_(r)+mv=0+0` [Both were at rest previously]
`rArrv_(t)=-(mv)/(M)`