Math CentralQuandaries & Queries


Question from mary, a student:

a car travelling at 50km/h stops in 4 seconds. how long (distance)did it take to stop?


The expression "distance = time × rate" applies if the rate remains constant.

50 km/h = 50 km/h × 1/60 h/min × 1/60 min/sec = 50/3600 km/sec and hence maintaining a speed of 50 km/hr for 4 seconds the car will travel 50/3600 × 4 = 5/90 km.

If the car is stopping its speed is decreasing and hence the distance travelled will depend on the rate at which the speed is decreasing.


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