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A motor car travelling at the rate of 40 km/hr is stopped by its brakes in 4 seconds. How long will it go from the point at which the brakes are first applied?

A motor car travelling at the rate of 40 km/hr is stopped by its brakes in 4 seconds. How long will it go from the point at which the brakes are first applied? Correct Answer 22(2/9)m

Let f be the uniform retardation in m/sec2 to the motion of the motor car due to application of brakes. By question, the car is stopped by its brakes in 4 seconds, hence, the final velocity of the car after 4 seconds = 0. Therefore, using the formula v = u – ft we get, 0 = ((40*1000)/(60*60) – f(4)) Or f = 25/9 Let the car go through a distance s m from the point at which the brakes are first applied. Then using the formula s = ut – 1/2(ft2) we get, s = ((40*1000)/(60*60))*4 – 1/2(25/9)(4*4) = 200/9 = 22(2/9) Therefore, the required distance described by the car = 22(2/9)m.

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