A machine gun with a mass of 5kg fires a 50g bullet at a speed of 100m/s. The recoil speed of the machine gun is 

Jamb 1978

A machine gun with a mass of 5kg fires a 50g bullet at a speed of 100m/s. The recoil speed of the machine gun is 

A. 0.5m/s

B. 1.5m/s

C. 1m/s

D 2m/s

E. 4m/s

ANSWER: Option C

EXPLANATION: When firing a gun, the gun’s momentum will be equal to the bullet’s momentum.

So, if Mg —> mass of the gun

         Vg —> recoil speed of the gun

         Mb —> mass of the bullet

         Vb —> speed of the bullet

Then, Gun momentum = Bullet momentum

Mg × Vg = Mb × Vb

Make Vg the subject of the formula and insert the values of the others to arrive at your answer.

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