A car at 90 km/h is 100 m behind another car going 72 km/h in the same lane. If both hold speed, how long until the gap is closed?
Answer and explanation
Correct answer: C. 20 s
- Step 1: Closing speed = 90 - 72 = 18 km/h = 5 m/s. Step 2. Time = 100 / 5 = 20 s. Answer: 20 s. Why not the others: 5.6 s: this divides 100 by 18, treating the km/h difference as m/s. 11.1 s: this comes from 100 / 9, a wrong conversion of the speed difference. 40 s: this uses half the closing speed.
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