A gun of mass 10kg fires a bullet of mass 240g at a speed of 300ms-1. What is the speed of the gun's recoil?

First, convert the mass of the bullet into SI units -> 240g=0.24kg

The law of the conservation of momentum states that m₁v₁=m₂v₂. To find the speed of the gun, rearrange for v₁ to give v₁=m₂v₂/m₁ and substitute in the given values; m₂=0.24kg, v₂=300ms^-1, and m₁=10kg. This gives v₁=0.24x300/10=7.2ms^-1