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Homework Help: Acceleration of a car followed by abrupt stop

  1. Sep 18, 2009 #1
    1. The problem statement, all variables and given/known data
    What is the acceleration of a vehicle that changes its velocity from 90 km/h to a dead stop in 13 s?

    2. Relevant equations

    i don't understand how to do this correctly

    3. The attempt at a solution

    i know im 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.
  2. jcsd
  3. Sep 18, 2009 #2
    Double check your units.
  4. Sep 18, 2009 #3
    you mean convert to meters?
  5. Sep 18, 2009 #4
    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).
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