ans is 60N
Mass of each bullet=m
Speedf each bullet=v
Number of bulllets fired per second=n
There fore exerted on the machine gun is,
f=mnv
The forece is directly proportional to rate of change of momentum
Therefore Per second the bullet fires,
f=mv
Since accelartaion ,a=v-u/t
u=0
t=1
a-v=0
Therefore Force by one bullet is mv
and force by n bullets is mnv
so F=0.02*10*300
=60N