A 100 g bullet moving horizontally at 400 m/s embeds itself into a stationary wooden block of mass 3.9 kg suspended by cords. What is the initial velocity of the block-bullet system immediately after impact?
Answer and explanation
Correct answer: B. 10.0 m/s
- Step 1: By conservation of linear momentum: m1 v1 + m2 v2 = (m1 + m2) V. Step 2. m1 = 0.10 kg, v1 = 400 m/s, m2 = 3.9 kg, v2 = 0. Step 3. (0.10)(400) = (0.10 + 3.9) V => 40 = 4.0 V => V = 10.0 m/s. Answer: 10.0 m/s. Why not the others:* 40 m/s forgets the total combined mass; 4 m/s divides by 10.
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