A gun of mass $4$ kg fires a bullet of mass $0.04$ kg at $300$ m/s. Recoil speed of the gun is:
A$3$ m/s, by $m_g v_g = m_b v_b$ with momentum zero
B$30$ m/s, equal to bullet speed scaled by mass ratio
C$0.3$ m/s, since recoil is one tenth of bullet speed
D$12$ m/s, equal to the product of bullet mass and speed
Answer & Solution
Correct answer: A. $3$ m/s, by $m_g v_g = m_b v_b$ with momentum zero
Conservation: $4\cdot v = 0.04\cdot 300 = 12$, so $v = 3$ m/s.
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