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Homework Help: Particles moving in a straight line

  1. Jul 27, 2012 #1
    A car moving with uniform acceleration along a straight level road, passed points A and B when moving with speed 6m s−1 and 14m s−1 respectively. Find the speed of the car at the instant that it passed C, the mid-point of AB.

    My working:

    acceleration from AB: v = u + at, 14-6 = at, 8/t = a

    distance from AB is:

    s =(6+14/2)t
    s = 5t

    as C is the midpoint of AB, s/2 = (5/2)t = AC

    so using u = 6, s = (5/2)t, a = 8/t, v = ?

    v^2 = u^2 + 2as
    v^2 = 36 + 2((8/t))((5/2)t)
    v^2 = 36 + 40
    v^2 = 76, v = 2root19, which is wrong

    any ideas?
  2. jcsd
  3. Jul 27, 2012 #2


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    Homework Helper
    Gold Member
    2017 Award

    Hi, phospho. Recheck the calculation for the steps shown above.
  4. Jul 27, 2012 #3
    eek, thanks.
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