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Homework Help: Confused on homework problem

  1. Oct 26, 2008 #1
    1. The problem statement, all variables and given/known data
    A 2450 kg car traveling to the west at 16.4 m/s slows down uniformly under a force of 8930 N to the east.
    a) How much force would be required to cause the same acceleration on a car of mass 3170 kg? Answer in units of N.

    2. Relevant equations

    3. The attempt at a solution
    I found in the first cart 2450x16.4 = 40,180 kg*m/s (the momentum)
    Since 8930 N is the same as 8930 kg*m/s^2
    40,180 / 8930 = 4.49900449 seconds

    I tried to use a similar with the second cart 3170 kg, but the problem is I don't know the force since i'm trying to find it I got stuck.
  2. jcsd
  3. Oct 26, 2008 #2


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    Gold Member

    4.49....s is the time it takes for the car to decelerate to a stop not the value of its acceleration.....dont you want to use F=ma for this question? ;0)
  4. Oct 26, 2008 #3
    That's what I thought too gabba, but then figured I was wrong to having it be a question.

    F = ma
    (-)8930 = 2450a
    a = -3.64 m/s^2

    F = ma
    F = (3170)(3.64 m/s^2)
    F ≅ 11,554 N
  5. Oct 26, 2008 #4


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    Looks good to me...the fact that they told you the initial speed was meant to throw you off.
  6. Oct 26, 2008 #5
    O I see I totally misread the question..... yea the intial speed threw me off.... i under stand it now. thanks a lot!!!
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