JAMB Physics 2020 Paper

Concept:The recoil of a gun follows the law of conservation of linear momentum.Explanation:Before firing, both the gun and bullet are at rest, so the total momentum is zero.After firing, the total momentum must still be zero.Therefore, the forward momentum of the bullet equals the backward momentum of the gun in magnitude.Convert the bullet mass to kilograms: $50\text{ g} = 0.05\text{ kg}$.Let the recoil speed of the gun be $v$.Use conservation of momentum:$$5v = 0.05 \times 100$$$$5v = 5$$$$v = 1\, \text{ms}^{-1}$$This matches option C.Answer:The recoil speed of the machine gun is $1\, \text{ms}^{-1}$.