A large spring is stretched by an athlete to increase the strength of his arms. The athlete extends the spring, as shown in Fig. 3.1, and then releases it gently. He extends and releases the spring several times during a period of 60 s. [Figure 3.1]

1. (a)State the form of energy stored in the stretched spring and the form of energy stored in the muscles of the athlete.[2]
2. (b)Suggest what happens if he extends the spring beyond the limit of proportionality.[1]
3. (c)(i)During one extension of the spring, its length increases from 70 cm to 93 cm. The average force exerted by the athlete is 400 N. Calculate the work done by the athlete in one extension.[2]
4. (c)(ii)Describe how the athlete can use the value obtained in (i) to determine his average power during the 60 s.[2]

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