Question

A pistol of mass 2 kg fires a bullet of mass 50 g.

The bullet strikes a stationary block of mass

1

2 kg.

If the block, with the bullet embedded in it, moves

with a velocity of 4 m/s, the recoil velocity of the

pistol will be (Ignore friction and air resistance)

Answer 1

answer will be 20m/s.
is it correct??
if yes then I will explain you.
tell me this answer is correct or not?

Answer 2

Case I

Bullet of mass 50g(=0.05kg) strikes a 1/2kg block.

So, m1= 0.05kg m2= 0.5kg

u1= ? u2= 0m/s

v1= 0m/s v2= 4m/s

Now,

m1u1+m2u2=m1v1+m2v2

0.05×u1+0.5×0=0.05×0+0.5×4

0.05×u1=2

u1= 2/0.05=40m/s

Case II

The pistol fires the bullet

Here let mass of pistol be m1 and that of bullet be m2

m1=2kg. m2=0.05kg

u1=0m/s. u2=0m/s

v1=? v2=40m/s

m1u1+ m2u2=m1v1+m2v2

0=2×v1+0.05×40

-2×v1=2

v1= -1m/s

Thus, the recoil velocity of the pistol is -1m/s.