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Car deceleration speed?

  1. Sep 13, 2008 #1
    Just wanted to clarify that this was the right way to calculate the deceleration when braking from a speed of 100km/h when the braking distance of the car is 45.73m.

    I am just using the formula v^2 = u^2 + 2as

    Which i have rearranged to find a...

    a = (v^2 - u^2)/2s ---------------- s = distance

    And I converted the 100km/h to m/s

    a = (0 - 27^2) / 2 * 45.73
    a = - 7.97ms/s

    Is that right???

    Or should I just leave the 100 in km...

    and then by deceleration is like -100ms/s?

  2. jcsd
  3. Sep 13, 2008 #2


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    Welcome to PF!

    Hi nic_nic344! Welcome to PF! :smile:

    Yes that's right … you get everything into the same units … except that your 27 isn't accurate enough. :wink:
  4. Sep 13, 2008 #3
    Yeh I will change the units to something like .78
    Thanks for your help!!
  5. Sep 13, 2008 #4
    real world the deceleration rate of a car is not steady state over the speed drop
    it starts low and gets higher as speed drops
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