A driver takes 20sec to apply the breaks after he sees a need for it . If he is driving car at a speed of 54km/hr and the break causes a deceleation of 6m/s², find the distance travelled by a car after he sees the need to put the break.

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Solution

Initial velocity of the car, u = 54 km/h = 15 m/s
He takes 20 s to hit the brake after he realizes of hitting it.
The deceleration of the car is 6 m/s².
So, after hitting the brake the car travels a distance says ‘S’.
Using,
v² = u² + 2aS
=> 0 = 15² + 2(-6)(S)
=> S = 18.75 m
The driver takes 20 s to hit the brake. In this 20 s the car travels (15)(20) = 300 m
So, the total distance the car travels after the driver sees that he needs to apply brake is = 300 + 18.75 = 318.75 m

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