Answer: it will take 5 hours before the second car overtakes the first
Explanation:
Let t represent the time it will take the second car to overtake the first car.
At the point where the second car overtook the first car, they would have covered the same distance. The first car leaves the town traveling at 72 km/h.
Distance = speed × time
Distance covered by the first car would be
72 × t = 72t
An hour later, a second car leaves the same town, on the same road, traveling at 90 km/h. It means that the time spent by the second car in travelling the same distance would be t - 1 hours. Therefore,
Distance covered by the second car would be
90(t - 1) = 90t - 90
Since the distance is the same,
90t - 90 = 72t
90t - 72t = 90
18t = 90
t = 90/18 = 5 hours