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P. 3994. A 60 kg boy notices a nice fruit on a tree. Even with stretched arms he cannot reach it, he is a 0.5 m below the fruit. The boy crouches down - his centre of mass descends 0.4 m - and then he leaps up. Thus he just reaches the fruit. Assume that he exerts a constant force on the ground while he touches it.

a) What is this force at least?

b) What is the average power of the boy?

(4 points)

Deadline expired on 11 October 2007.

Statistics on problem P. 3994.
 282 students sent a solution. 4 points: 113 students. 3 points: 10 students. 2 points: 61 students. 1 point: 55 students. 0 point: 38 students. Unfair, not evaluated: 5 solutions.

• Problems in Physics of KöMaL, September 2007

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