Posted by **David** on Wednesday, February 6, 2008 at 3:12am.

The brakes on a car permit it to decelerate at the rate of -8.0m/s^2. How much distance is required to stop this car when it is travelling 60.0km/hr?

The answer given is 173.6m

I solved it this way

60km/h = 16.667m/s

A=V/T 16.667m/s / -.80m/s^2 = 20.834 seconds

D=RT 16.667m/s x 20.834seconds = 347.24m

This is wrong and I do not understand why. Am I doing it right or is the answer wrong?

- Physics 11 -
**bobpursley**, Wednesday, February 6, 2008 at 7:29am
The last equation....

distance= rate/time. You need the average velocity, not the initial. Average here is 1/2 the initial.

- Physics 11 -
**Binh-An**, Wednesday, February 6, 2008 at 10:12am
Hi, I'm very familiar with math. I'm 11, and I'm the king of math of my class. Your answer is twice as much as the given answer, David. Hey there, you got the second equation wrong. For the divisor you are supposed to have the time, not the acceleration. Try solving for the time by knowing about integrals (F(a)=v; F(v)=t; this is tricky, I hope it works).

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