A 10 kg body dropped from a height of 20 m reaches speed 10 m s⁻¹ after falling 20 m. Find work done by air on the body. Take g=10 m s⁻².
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Question

A 10 kg body dropped from a height of 20 m reaches speed 10 m s⁻¹ after falling 20 m. Find work done by air on the body. Take g=10 m s⁻².

G1 Physics · Accepted Answer

Step 1 — Principle: The net work on a body equals its change in kinetic energy: Wₙₑₜ = Kf − Ki. Step 2 — Working: Gravity work mgh=10×10×20=2000 J; final KE=½×10×10²=500 J. Step 3 — Working: Total work=500 J, so air work=500−2000=−1500 J. Correct answer: C — −1500 J.