A hazard appears 30 m ahead of a car travelling at 54 km/h. The driver reacts after 1 s and brakes at 3 m/s squared. How far past the hazard's position does the car stop?

Answer and explanation

Correct answer: B. 22.5 m

  1. Step 1: Speed = 15 m/s; thinking distance = 15 x 1 = 15 m; braking distance = 15 squared / (2 x 3) = 37.5 m, so stopping distance = 52.5 m. Step 2. The car needs 52.5 m but only 30 m are free, so it stops 52.5 - 30 = 22.5 m beyond the hazard's position. Answer: 22.5 m. Why not the others: 37.5 m: 37.5 m is the braking distance alone, leaving out the thinking distance and the gap. 52.5 m: 52.5 m is the whole stopping distance, with no allowance for the 30 m gap. 82.5 m: 82.5 m adds the gap instead of subtracting it.

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