Minimum deaceleration untll the car stops

[forensicchemgirl]

what am i doing wrong??
every time i try to answer this i get t=.2s and a=-1651ms^-2

the problem reads...
A car traveling at 25mi/h is to stop on a 35m-long shoulder of the road. (a) What is the required magnitude of he minimum acceleration? (b)How much time will elapse during this minimum deaceleration untll the car stops.

i used the equation...
a=v^2/2x

 

[physicsgal]

i think the first time is to convert 25mi/h into meters per second.

~Amy

 

[Tomsk]

Yes, use 1 mile =1.6km, and don't forget to convert to m/s, so you need to change out of km/h. 1h=3600s. That equation is right.

 

[forensicchemgirl]

yes i did convert to m/s wrong thanks for the help.