# Question about constant acceleration

1. May 27, 2006

### elizabethR

how would i do this problem...

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.

1)How far are you from the intersection when you begin to apply the brakes? I know this answer: 100m.
...i can't figure out the next two. please help me figure out the formula for this!
2)What acceleration will bring you to rest right at the intersection?
3)How long does it take you to stop?

2. May 28, 2006

### andrevdh

2) You know what distance, $x=+100\ m$, you have to travel to come to a halt, $v=0$, at the traffic light. You also know what velocity you start out with, $v_o=+20\ m/s$, when you apply the brakes at the beginning of the deceleration.

Last edited: May 28, 2006
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