Question

From a rifle of mass 4 kg, a bullet of mass 50 g is fired with an initial velocity of 35 m/s. calculate the initial recoil velocity of the rifle. (class 9th)(3 marks)

Answer 1

before firing,
m1=4kg
u1=0
momentum=m1×u1
=4×0
=0
m2=50g
=0.05 kg
u2=0
momentum=m2×u2
=0.05+0
=0kgm/s
total momentum before fire=0
after firing,
m1=4kg
v1=?
momentum=4×v1
m2=0.05
v2=35m/s
momentum=m2×v2
=0.05×35
=1.75kgm/s
total =4v1+1.75
according to law of conservation of momentum
m1u1+m2u2=m1v1+m2v2
0=4v1+1.75
4v1+1.75=0
4v1= -1.75/4
4v1= -1.75
v1=1.75/4
v1=-0.4375m/s

Answer 2

ANSWER :

( m₁ ) Mass of rifle = 4kg

( m₂ ) Mass of bullet = 50g = 0.05kg

( v₂ ) Velocity of bullet = 35 m/s

( v₁ ) Recoil velocity of rifle = ?

ACCORDING TO THE LAW OF CONSERVATION OF MOMENTUM :

Momentum of rifle    =    Momentum of bullet

             m₁v₁              =   m₂v₂

        4kg × v₁             =     0.05 × 35 m/s

          v₁                     =   0.05 × 35  / 4     = 1.75/4

          v₁                     =   0.4375 m/s

Therefore,   Recoil velocity of rifle =  0.4375 m/s