Question

A bullet leaves a rifle with a velocity of 5m/s and the rifle of mass 2.5kg recoils with a velocity of 1m/s. Find the mass of the bullet

Answer 1

Momentum is mass in motion,  i.e. p = m*v

Acc. to law of conservation of momentum-

                p1 = p2
i.e.   m1 * v1 = m2 * v2   [where m is mass and v is velocity]

now let- 
m1 = mass of rifle           ;    v1 = recoil velocity
m2 = mass of bullet       ;    v2 = mass od bullet


Acc. to question-
                    m1 * v1         =    m2 * v2 
             2.5 kg * 1 m/s     =     m2 * 5m/s
  i.e.       2.5 kg * 1 m/s    =     m2  
                  5m/s
                         0.5 kg     =     m2

Answer: The mass of the Bullet is 0.5 kg.