A gun weighing `9kg` fires a bullet of `30g` with a velocity of `300m//s` What is the recoil velocity of the gun? What is the combined momentum of gun and the bullet before and after firing ?

Answer

`1m//s; Zero; Zero` .

Explanation

Here, `m_(1) = 9kg, m_(2) = 30 g = 30 xx 10^(3) kg`
`upsilon_(2) = 300 m//s, upsilon_(1) = ? P_(1) = ? P_(2)= ?`
As `m_(1) upsilon_(1) + m_(2) upsilon_(2) =0`
`upsilon_(1) = - (m_(2) upsilon_(2))/(m_(1))=- (30 xx 10^(3) xx 300)/(9) = - 1m//s`
Negative sign indicates recoil velocity Before firing the gun and bullet both are at rest and so is the case after firing Therefore their combined momentum in either case is zero.