A car at 40 km/h needs 2 m to stop using a given braking force. What stopping distance is needed at 80 km/h with the same brakes?
Options

Question

A car at 40 km/h needs 2 m to stop using a given braking force. What stopping distance is needed at 80 km/h with the same brakes?

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: Brake work Fs removes KE ½mv². Step 3 — Working: With unchanged force, s∝v². Step 4 — Working: Speed doubles, so stopping distance becomes 4×2=8 m. Correct answer: A — 8 m.