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A body of mass 100 g is projected straight upward with an initial speed of 5 m/s. The work done by gravity while the body is moving upward is

1. -0.5 J
2. -1.25 J
3. 1.25 J
4. 0.5 J

Correct answer: -1.25 J

Solution

The stone rises to h = u^2/(2g) = 25/20 = 1.25 m. While moving upward, gravity acts opposite to motion, so W = -mgh = -(0.1)(10)(1.25) = -1.25 J.

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