A wire suspended vertically from one end is stretched by attaching a weight of 20N to the lower end. The weight stretches the wire by 1mm. How much energy is gained by the wire ?
Correct answer: A. 0.01J
- A. 0.01J
- B. 0.02J
- C. 0.04J
- D. 1.0J
Explanation
The wire's elastic energy is the area under its linear force-extension graph: E = 1/2 x F x x = 1/2 x 20 N x 0.001 m = 0.010 J. The likely mistake is 0.02 J, which uses F x x and forgets that the force increases gradually from 0 N to 20 N.
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