AS Daily A Level Physics question
A car on a level road is brought to rest by a constant braking deceleration. If the initial speed is doubled (same braking force so the deceleration is unchanged), what happens to the stopping distance?
Answer
The correct answer is C.
Correct: C — It increases by a factor of four. Under constant deceleration to rest, stopping distance depends on the square of the initial speed, so doubling the speed makes the distance four times larger. A is wrong because it assumes a linear relationship with speed; the dependence is quadratic, not proportional. B is wrong because greater initial speed cannot give the same stopping distance with the same deceleration. C is correct as distance ∝ (initial speed)^2 when deceleration is fixed. D is wrong because the stopping distance does not decrease when starting faster.