Question

a bullet leaves a rifle with a velocity of 100m/s and the rifle of mass 2.5kg recoils with a velocity of 1m/s. find the mass of the bullet.

Answer 1

let the mass of thr bullet be x

momentum of the gun = momentum of the bullet

(2.5)(1) = (100)(x)

2.5 = 100x
x = 0.025

so, the mass of the bullet was 0.025kg or 25 grams

Answer 2

we know that by conservation of linear momentum , 

v2= m1/m2*v1
1= m1/2.5*100
1/100= m1/2.5
2.5/100=m1
m1=25/1000
m1=1/40=0.025kg