A 100kg block is dropped from the top of a building 80m tall. Assume g=10ms−2. Find the work done by the force of gravity as it falls vertically to hit the ground.
A
80000J
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B
−80000J
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C
20000J
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D
0J
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Solution
The correct option is A80000J We know that, Workdone, W=→F.→s
F=mg=100×10=1000N;s=80m W=FScosθ, as it is falling vertically the force of gravity is along the direction of displacement (cos0o=1)