An object of mass 5kg falls from rest through a vertical distance of 20m and reaches a velocity of 10m/s. How much work is done by the push of the air on the object?
−740J
−750J
−770J
−760J
A
−740J
B
−750J
C
−760J
D
−770J
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Solution
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From work energy theorem,
work done by weight + work done by
air=ΔKE (change in Kinetic Energy)
Wair=ΔKE−W(weight)
=12mv2−mgh
=12×5×(10)2−5×10×20
=−750J
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