Question

From a rifle of mass 5 kg, a bullet of mass 50g is fired with an initial velocity 05
of 108 km/h. Calculate initial recoil velocity of the rifle.

Answer 1

conservation of linear momentum

when external force act on system = 0 , linear momentum of system remains constant.

I mean, initial momentum = final momentum

here mass of rifle , M = 5Kg

mass of bullet , m = 50gm = 0.05kg

initial velocity of bullet , u = 50 m/s

we have to find initial recoil velocity of rifle , U

final velocity of bullet , v = 0

final velocity of rifle , V = 0

use conservation of linear momentum,

mu+MU=mv+MVmu+MU=mv+MV

0.05 × 50 + 5 × U = m × 0 + M × 0

0.05 × 50 + 5U = 0

5U = -0.05 × 50

U = -0.5 m/s [here negative sign shows that velocity of rifle is just opposite to the bullet .

hence, initial velocity of refile is -0.5 m/s