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Question
A shell of mass 0.020 kg is fired by a gun of mass 100 kg. If the muzzle speed of the shell is 80 m s–1, what is the recoil speed of the gun?
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Solution
Mass of the gun, m2 = 100 kg
Mass of the shell, m1 = 0.020 kg
initial velocities of both the shell and the gun are zero u1 = u2 = 0
After firing, the speed of the shell, v1 = 80 m s-1
Let v2 represent the recoil velocity of the gun. Following the principle of conservation of momentum,
m1v1 + m2v2 = m1u2 + m2u2
0.02 x 80 + 100v2 = 0.02 x 0 + 100 x 0
`v_2 = - 0.02xx80/100 = -0.016 "ms"^(-1)`
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