You are driving to the grocery store at 20 m/s. You are 110 m from an intersecti

Question

You are driving to the grocery store at 20 m/s. You are 110 m from an intersection when the traffic light turns red. Assume that your reaction time is 0.50 s 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 to two significant figures and include the appropriate units.

Part B:

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

Express your answer to two significant figures and include the appropriate units.

Part C:

How long does it take you to stop after the light turns red?

Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

A. 110 - (20 x 0.50) = braking distance = 100.0 m

b) What acceleration will bring you to rest as you just reach the intersection?

v^2 = 0 = u^2 + (2as)

u^2 = 20^2 = 400

2as = - 400

400/ (2 x 100) = a = 2.0 m/s^2

c)
How long does it take you to stop?

u + at = 0

20/ 2.0 = t = 10 secs

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