A 10 kg block initially travelling at 10 m s⁻¹ is subjected to a retarding force of magnitude 0.1x N while travelling from x=20 m to x=30 m. Find its final kinetic energy.
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Question

A 10 kg block initially travelling at 10 m s⁻¹ is subjected to a retarding force of magnitude 0.1x N while travelling from x=20 m to x=30 m. Find its final kinetic energy.

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: Initial KE=½(10)(10²)=500 J. Step 3 — Working: Retarding work W=−∫₂₀³⁰0.1x dx=−0.05(30²−20²)=−25 J. Step 4 — Working: Final KE=475 J. Correct answer: A — 475 J.