Question 9
Work, Energy and PowerA bullet fired at a wooden block of thickness 0.15 m manages to penetrate the block. If the mass of the bullet is 0.025 kg and the average resisting force of the wood is 7.5 × 103 N, calculate the speed of the bullet just before it hits the wooden block.
- A.450 m s−1
- B.400 m s−1
- C.300 m s−1
- D.250 m s−1
Show the answer and explanation
Answer: C (300 m s−1)
Explanation
The bullet's kinetic energy is used up against the wood: ½ × 0.025 × v2 = 7.5 × 103 × 0.15 = 1125 J, so v2 = 90 000 and v = 300 m s−1.