A driver travels with a constant initial speed of 25.0 m/s when he sees an obstr

Question

A driver travels with a constant initial speed of 25.0 m/s when he sees an obstruction in the road ahead at a distance of 50.0 m. It takes the driver 0.75 seconds to react to the obstruction before hitting the brake. His tires have a 0.8 coefficient of static friction with the road.

a.How far will the car travel before hitting the brake?

b.What will the acceleration of the car be after hitting the brake?

c.How far will the car travel before it is able to stop? (ie, will it be able to stop in time?)

Explanation / Answer

Ans (a)

t=0.75 , u=25

s=ut+1/2 at2 (speed constant a=0 thats why 1/2at2 is 0 )

s=25*0.75

s=18.75 mtr

Ans (b)

V=0 , u=25

v2=u2+2as

a=25*25 / 2*18.75

a=16.66 m/s2

Ans (c)

because in 0.75 sec cross 18.75 so

in 1 sec 18.75/0.75

then in 1.58 sec 18.75/0.75*1.58 = 39.5 M

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