You are driving to the grocery store at 24 m/s. You are 130 m from an intersecti

Question

You are driving to the grocery store at 24 m/s. You are 130 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.
What acceleration (magnitude) will bring you to rest right at the intersection?
How long (total) does it take you to stop after the light turns red?

I figured out that you will begin braking after 12 m, so then the distance between the car and the light is 118 m. How do I calculate magnitude and then time as the car decelerates?

Explanation / Answer

initial velocity u = 24 m/s distance S= 130 m final velocity v = 0 reaction time t = 0.50 s acceleration (magnitude) will bring you to rest right at the intersection a = ? from the relation v^2- u^2 = 2aS from this accleration a = ( v^2 - u^2 ) / 2S = -2.215 m / s^ 2 time taken to stop t ' = ( v- u ) / a = 10.83 s

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