a bullet of mass 5g is fired using a gun of 2 kg. the velocity of the bullet is 36km/hr. what is the velocity of the gun?

Question

anonymous · Answer

Conservation of momentum: Initially both gun and bullet are at rest thus momentum P=0
After words momentum = mass bullet * velocity + mass gun*velocity of gun = 0 since momentum is conserved. 
Thus mass bullet * velocity of bullet = - mass gun * velocity of gun 
velocity of gun = - mass bullet * velocity of bullet / mass gun 
v_gun= - 5g*36kg/hr /2000g= -0.09 km/hour 
negative sign indicates in opposite direction of bullet

anonymous · Answer

By newton's third law and law of conservation of momentum we can have both the forces balancing
hence
$$5*10^{-3}*(36*5/18)=(2*velocity of gun)$$
velocity of gun=0.025m/s

anonymous · Answer

5 * 35 = 2000 * v

anonymous · Answer

-0.09Km/h