A 4 kg rifle fires a 20 g bullet with a muzzle speed of 400 m/s. What is the recoil speed of the rifle?
Correct answer D. 2 m/s
Explanation
Momentum is conserved from rest: m_b v_b = m_r v_r, so v_r = (0.020 × 400)/4 = 2 m/s. Forgetting to convert 20 g to kg gives a huge error.
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