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A driver takes 0.20 s to apply the brake...

A driver takes 0.20 s to apply the brakes after he sees a need for it. This is called the reaction time of the driver. If he ils driving a car at a speed of 54 km/h and the brakes cause a deceleration of `6.0 m/s^2`, find the distance travelled by the car after he sees the need to put the brakes on.

Text Solution

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Distance covered by the car during the application of brakes by driver
`s_(1)=ut=(54xx5/18)(0.2)=15xx0.2=3.0 m`
After applying the brakes, `v=0, " "u=15 m//s, a=6 m//s^(2) s_(2)=?`
Using `v^(2)=u^(2)-2as rArr 0=(15)^(2)-2xx6xxs_(2)rArr 12 s_(2)=225rArr s_(2)=225/12=18.75 m`
Distance travelled by the car after driver sees the need for it `s=s_(1)+s_(2)=3+18.75-21.75 m`
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