You are driving to the grocery store at 19m/s . You are 120m from an intersectio

Question

You are driving to the grocery store at 19m/s . You are 120m from an intersection when the traffic light turns red. Assume that your reaction time is 0.70s and that your car brakes with constant acceleration.

Part A

How far are you from the intersection when you begin to apply the brakes?

Express your answer using two significant figures.

Part B

What acceleration will bring you to rest right at the intersection?

Express your answer using two significant figures.

Part C

How long does it take you to stop?

Express your answer using two significant figures.

Explanation / Answer

PART A

It is 0.70 seconds(reaction time) for which the car moves at 19 m/s before the breaks are applied.

so, distance covered = 19 * 0.70 = 13.30 m

Thus distance of car from signal = 120 - 13.30 = 106.70 m

PART B

To be at rest at the intersection, we have;

final velocity = =

initial velocity = 19

distance to cover = 106.70

using the equation v2 = u2 + 2as where v is final velocity , u is initial velocity , s is distance travelled and a is acceleration(negative in this case), so

0 = 361 + 2*a*106.70

a = - 361/213.40

a = -1.69 m /s2

PART C

to find the time, we use the equation==> v = u + at

0 = 19 -1.69t

t = 11.24s

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