A machine gun of mass 10 kg, fires 10 gm bullets with a velocity of 400m/s at the rate of one every second. The velocity of recoil of the gun after four bullets are fired is 

1) 0.4 m/s

2) 0.8 m/s ND 

3) 1.6 m/s 

4) 3.2 m/s 1 Level-3