Zachary is on the left in the figure (Hand 1), and Zoey is on the right (Hand 2)

Question

Zachary is on the left in the figure (Hand 1), and Zoey is on the right (Hand 2). Zachary presses down on the bar as hard as he can. In Fig.-1a, Zoey has to use all her strength to lift Zachary's hand a distance, h. In Fig.-1b, Zoey barely has to strain herself at all and she's able to easily raise Zachary's hand the same distance, h. Explain from a detailed, physics point of view why that's so. You cannot use the concept of torque or leverage. The idea is to explain those concepts in other terms.

Explanation / Answer

In case 1) Hand 2 (i.e. Zoey's Hand) has less potential energy than Hand 1 ( Zachary's Hand) So it can not raise Hand 1 up to a height where final potential energy is more than the initial potential energy.

But In case 2) Hand 2 (i.e. Zoey's Hand) has more potential energy than Hand 1 ( Zachary's Hand) So it can easily raise Hand 1 up to a height where final potential energy is less than the initial potential energy.

This all can be explained on the basis of law of conservation of energy.

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