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Homework Help: Check work on kinematics problem

  1. Apr 27, 2012 #1
    1. The problem statement, all variables and given/known data
    A truck accelerates uniformly from rest to 48km/h in 20s, holds speed for 2 minutes, and then accelerates to 100km/h at a rate of 17m/s^2. How long does it take, from rest, to reach 100km/h and what distance it traveled in this time?

    The book says it takes 148.5s, and I keep getting 140.85s.
    For distance the book says 1904m, and I been getting lower at 950.57m.

    I was hoping someone could just check the answers for me, since I am doing a course from a book that has had alot of mistakes thus far, if it turns out that my answers are wrong I will post my what I've been doing to get some help on it. Thanks much!
  2. jcsd
  3. Apr 27, 2012 #2
    Hey Caperjay, could you post some work? Then we'll see what's up.
  4. Apr 27, 2012 #3
    Heres what I've done. For the total time I got 20s + 120s + (13.33=27.78 + 17m/s^2xt) where t turns out to be 0.85s, for a total of 140.85s.

    For total distance I've got (0+13.33)/2 x 20s + (13.33 + 13.33)/2 x 120s + (13.33 + 27.78)/2 x 0.85s, for a total of 950.57m.
  5. Apr 28, 2012 #4
    "at a rate of 17m/s^2"

    Mighty powerful truck!
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