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Homework Help: Constant Acceleration Problem

  1. Sep 16, 2007 #1
    1. The problem statement, all variables and given/known data
    At the instant the traffic light turns green, a car that has been waiting at an intersection starts ahead with a constant acceleration of 2.80 m/s^2. At the same instant a truck, traveling with a constant speed of 17.0 m/s, overtakes and passes the car.

    How far beyond its starting point does the car overtake the truck?

    2. Relevant equations
    One of the four constant acceleration equations

    3. The attempt at a solution
    I honestly have no idea how to start this, but I think I need a graph to solve.
  2. jcsd
  3. Sep 16, 2007 #2


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    Gold Member

    You do not need a graph to solve this problem, but a picture always helps.

    In order to get help on this forum you need to show some work.

    Can you list the variables you know and don't know?
    Can you give me the equations of motion for one or both of the vehicles?

    Give me something so I can know what is confusing you.
  4. Sep 16, 2007 #3
    Well, I'm a bit lost on this question but here goes.

    I think I use the equation X = 1/2*a*t[tex]^{2}[/tex] because X initial and V initial are 0.Of course I don't know how helpful this is as I don't have the time.

    All I know is the constant velocity is 17 m/s. The truck overtakes the car at X=0

    The intersection is X=0 and t=0.

    I need to know the distance it takes the car to overpass the truck, and at what velocity.

    Again, I'm not to sure of the accuracy of this post
  5. Sep 16, 2007 #4
    your post is accurate,
    now, what is the equation of the coordinate X1 of the truck in fuction of time ?

    now the truck intersects the car at t=0 X=0, that's true, but we need the second intersection time and distance.

    let X(t) the coordinate of the car, let X1(t) the coordinate of the trucks,
    what's the relation between X(t) and X1(t) when the car and truck intersect again ?
  6. Sep 16, 2007 #5


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    As tabchouri said, this sounds good. Now, what do we know about the x coordinates of both vehicles when they intersect?
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