A 10 g bullet travelling horizontally at 400 m s⁻¹ passes through a stationary 2 kg wooden block suspended as a pendulum. The block rises by 10 cm. Find horizontal speed of the emerging bullet (g=9.8 m s⁻²).
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Question

A 10 g bullet travelling horizontally at 400 m s⁻¹ passes through a stationary 2 kg wooden block suspended as a pendulum. The block rises by 10 cm. Find horizontal speed of the emerging bullet (g=9.8 m s⁻²).

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G1 Physics · Accepted Answer

Step 1 — Principle: A short collision conserves linear momentum, whereas kinetic energy may be lost to other forms. Step 2 — Working: From block rise h=.1 m, its speed immediately after collision is V=√(2gh)=√(1.96)=1.4 m/s. Step 3 — Working: Horizontal momentum: .01×400=.01 v+2×1.4; hence .01 v=1.2, v=120 m/s. Correct answer: C — 120 m s⁻¹.