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Kinematics problem that i cant seem to resolve

  1. Sep 5, 2011 #1
    1. The problem statement, all variables and given/known data

    A truck starts from rest and accelerates at 1 M/S*2 . 4 s later, a car accelerates from rest at the same starting point with an acceleration of 2.7 M/S*2 .

    Where and when does the car catch the truck?

    2. Relevant equations


    i have tried s=ut + (1/2)at^2
    3. The attempt at a solution
    In 4 seconds, truck travels a distance of 0 (4) + (1/2) (1) (4)^2 = 0 + 8 = 8

    now, when car starts, truck is already 8 m ahead of it.

    Suppose they meet at time lapse of t seconds after car starts.
    So, car travels 8 m more than the truck in t seconds.
    distance travelled by car in t seconds = dist travelld by truck in t seconds + 8

    0 (t) + (1/2) (2.7) (t)^2 = 0 ( t) + (1/2) (1) (t)^2 + 8

    ==> (t)^2 = (160) / 17
    t = 3.06

    hence, car catches truck at 4 + 3.06 = 7.06 seconds after truck starts.
    distance travelled by car = 0 (7.06) + (1/2) (4) ( 160/17) = 18.8 metres, but thats not the anwser :s
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 5, 2011 #2

    lewando

    User Avatar
    Gold Member

    Yo, why 2 threads? I know, in theory it should speed things up :tongue:.
     
  4. Sep 5, 2011 #3
    The distance the truck travels will equal the distance the car travels. Try setting your distance formulas equal to each other and see what you get.
     
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