# Consider a car moving along a straight horizontal road with a speed of 72km/h. If the coefficient of static friction between the tyres and the road is 0.5, the shortest distance in which the car can be stopped is? (g=10m/s^2)

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Consider a car moving along a straight horizontal road with a speed of 72km/h. If the coefficient of static friction between the tyres and the road is 0.5, the shortest distance in which the car can be stopped is? (g=10m/s^2)

(a) 30m

(b) 40m

(c) 72m

(d) 20m

The question was posed to me in an international level competition.

This intriguing question originated from Friction and Motion topic in section Laws of Motion of Engineering Physics I

## 1 Answer

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Correct option is (b) 40m

For explanation I would say: Retardation, a = -μg = -0.5×10 = -5m/s^2

u = 72km/h = 20m/s

As v^2-u^2=2as

s = 40m.

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