A rifle of 20 kg mass can fire 4 bullets/s. The mass of each bullet is `35xx10^(-3)kg` and its final velocity is `400ms^(-1)`. Then, what force must be applied on the rifle so that it does not move backwards while firing the bullets

Explanation

Law of conservation of momentum,
`MV+4mv=0`
`rArr V=-(4mv)/(M)=(4xx35xx10^(-3)xx400)/(20)=-2.8ms^(-1)`
Force applied on the rifle
`F=(MV)/(t)=-(20xx2.8)/(1)=-56N`