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Homework Help: Finding the time it takes to stop

  1. Nov 16, 2007 #1
    1. The problem statement, all variables and given/known data

    A 2410 kg car traveling to the west at 22.6 m/s slows down uniformly.

    How long would it take the car to come to a stop if the force on the car is 8880 N to the east? Answer in units of s

    What is the car's displacement during the time it takes to stop? Answer in m

    2. Relevant equations

    d = .5at^2 + Vit

    3. The attempt at a solution

    2410 * 22.6 = 54466 kg*m/s (the momentum)

    8880 N is also 8880 kg*m/s^2

    54466 / 8880 = 6.133558559 seconds (this is right)

    d = .5at^2 + Vit
    d = (.5)(22.6/6.13355)(6.13355^2) + (22.6*6.13355)
    d = 207.9273 m

    I got the time, but when i plug in the displacement it's wrong
    Last edited: Nov 16, 2007
  2. jcsd
  3. Nov 16, 2007 #2


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    Science Advisor
    Gold Member

    The acceleration is directed opposite to the initial speed, so you must be careful about signs.
  4. Nov 16, 2007 #3
    Last edited: Nov 16, 2007
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