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Homework Help: Constant Acceleration Automobile

  1. Jan 23, 2008 #1
    [SOLVED] Constant Acceleration

    1. The problem statement, all variables and given/known data

    At the instant the traffic light turns green, an automobile starts with a constant acceleration a of 2.1 m/s^2. At the same instant a truck is 10.2 m down the road and traveling with a constant speed of 8.5 m/s. (a) How far beyond the traffic signal will the automobile overtake the truck? (b) How fast will the automobile be traveling at that instant?

    2. Relevant equations



    3. The attempt at a solution

    s(t) = 1/2 a * t^2 + v0 * t + s0
    a = acceleration
    v0 = initial speed
    s0 = initial position


    Being for the truck
    a = 0 m/s^2
    v0 = 8.5 m/s
    s0 = 10.2 m
    and being for the car
    a = 2.1 m/s^2
    v0 = 0 m/s
    s0 = 0 m
    the equation will be:
    8.5 m/s * t + 10.2 m = (There is a 1/2 here right?) (1/2)2.1 m/s^2 * t^2

    Solving this I get 9.156s which is apparently incorrect.
     
  2. jcsd
  3. Jan 23, 2008 #2

    G01

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    Gold Member

    I believe the equation you set up is correct. Can you show your math?
     
  4. Jan 23, 2008 #3
    Well the math is kinda already there QQ I just plugged it into quadratic equation.
     
  5. Jan 23, 2008 #4
    OK I got it!

    s(9.16) = 1/2 (2.1) * (9.16)^2 = 88.1 meters

    and after 9.16 seconds, it is traveling
    v = at
    v = 2.1(9.16) = 19.2 m/s
     
  6. Jan 23, 2008 #5

    G01

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    Awesome! Good job!
     
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