Question

# A stone weighing 1 kg is dropped from rest from a height of 4 metres above the ground. When it has free-fallen 1 metre its total energy with respect to the ground is

A

30 J

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B

40 J

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C

20J

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D

15J

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Solution

## The correct option is B 40 J Energy is conserved in free-fall situations (no external forces doing work). Thus, the total energy would be same at every stage in falling. Whatever total energy body has initially, it will maintain it throughout the course of its motion. PE = mgh = 1 x 10 x 4 = 40 J The object begins with 40 J of potential energy and no kinetic energy. The total mechanical energy (KE + PE) is 40 J.

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