(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

You are driving to the grocery store at 16 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.

x1 = 0 m

v1 = 16 m/s

t1 = 0 s

x2 = ?

v2 = 16 m/s

t2 = 0.50s

x3 = 130 m

v3 = 0 m/s

t3 = ?

2. Relevant equations

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

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

(c) How long does it take you to stop?

3. The attempt at a solution

for (a)

(x2-x1) = ((v1+v2)/2)*(t2-t1)

(x2-0m)=((16m/s+16m/s)/2)*(0.50s-0s)

x2=(32m/s/2)*0.50s

x2=16m/s*0.50s

x2 = 8m

for (c)

(x3-x2) = ((v2+v3)/2)*delta t

122m=(16m/s/2)*delta t

16s=delta t

for (b)

a=delta v/delta t

a=-16m/s/16s

a=-1 m/s^2

I know (a) is correct, where I am having issues is computing the final time so I can then obtain the acceleration.

Thanks,

Bracing

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Issues finding time in acceleration problem

**Physics Forums | Science Articles, Homework Help, Discussion**