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JAMB Physics 1978 Question 7

Question 7

Newton's Laws and Momentum

A machine gun with a mass of 5 kg fires a 50 g bullet at a speed of 100 m s−1. The recoil speed of the machine gun is

  1. A.0.5 m/sec
  2. B.1.5 m/sec
  3. C.1 m/sec
  4. D.2 m/sec
  5. E.4 m/sec.
Show the answer and explanation

Answer: C (1 m/sec)

Explanation

Momentum is conserved: 5 × v = 0.05 × 100 = 5, so the gun recoils at v = 1 m/s.