AS Daily A Level Physics question
A car on a dry test track brakes with the same constant deceleration each time. If the initial speed is doubled, what happens to the braking distance before it stops? Assume reaction time is zero and ignore air resistance.
Answer
The correct answer is B.
Correct: B — It becomes four times as large. For the same uniform deceleration to zero, stopping distance depends on the square of the initial speed, so doubling speed makes the distance four times bigger. A assumes a linear dependence on speed rather than a square dependence. B is correct because with constant deceleration the distance to stop scales with the square of the initial speed. C picks an arbitrary factor that does not follow from uniform deceleration. D ignores the clear dependence of stopping distance on initial speed.