Acceleration of a car followed by abrupt stop

[iluvpandas]

Homework Statement

What is the acceleration of a vehicle that changes its velocity from 90 km/h to a dead stop in 13 s?

Homework Equations

i don't understand how to do this correctly

The Attempt at a Solution

i know I am supposed to use the formula for acceleration [a= (Vi-Vf)/T] i plugged in 90 for the Vi and 0( the dead stop) for Vf after that i divided by 13 but the answer i got was wrong.

 

[physicsface]

Double check your units.

 

[iluvpandas]

you mean convert to meters?

 

[physicsface]

No. Your velocity is given in km/h and your time is given in s; they need to coordinate before you can just plug them in. You need to either convert your time to hours (in which case acceleration units would be km/h²) or convert your velocity to km/s (acceleration would be in km/s²).