From a rifle of mass 4 kg, a bullet of mass 50 g is fired with a velocity of 35 ms−1 with respect to the ground. Calculate the recoil velocity of the rifle.
0.4375 ms−1
Let initial velocity of bullet be u1 and initial velocity of rifle be u2.
u1 =u2 =0 (Initially bullet and rifle system was at rest)
Let, mass of rifle ,m1 = 4kg
Mass of bullet, m2 = 501000=0.05kg
Final velocity of bullet, v2 = 35 ms−1
Final velocity of rifle, v1 = v
From principle of conservation of linear momentum:
Initial momentum is equal to final momentum.
m1u1+m2u2=m1v1+m2v2
4×0+0.05×0=4×v+0.05×35
0=1.75+4v
⇒v=−0.4375 ms−1
The negative sign indicates that the rifle recoils in the opposite direction with the velocity of 0.4375 ms−1.