A bullet of mass 100g is fixed from a gun of mass 20kg with a velocity of `100 ms^-1` Calculate the velocity of recoil of the gun.

Explanation

Mass of bullet `m=100g=100/1000 kg =1/10 kg`
velocity of bullet `v=100 ms^-1`
Mass of gun M=20 kg
Let recoil velocity of gun =V
Step 1: Before firing, the system is at rest, therefore initial momentum of the system =0
Final momentum of the system= momentum of bullet+ momentum of gun
`mv+MV=1/10 times 100+20V=10+20V`
Step 2: APply law of conservation of momentum Final momentum= Initial momentum
i.e., 10+20V=0
`20V=-10`
or `V=- 10/20=-0.5 ms^-1`
Negative sign shows that the direction of recoil velocity of the gun in opposite to the direction of the velocity of the bullet.