Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: At the instant when the traffic light turns green, a car starts with a constant accel

  1. Oct 10, 2011 #1
    1. The problem statement

    At the instant when the traffic light turns green, a car starts with a constant acceleration of 1.8 m/s^2 [forward]. At the same instant a truck traveling with a constant velocity of 8.5 m/s [forward] overtakes and passes the car. How far from the starting point will the car catch up to the truck?



    2. The attempt at a solution
    Car:
    d = V1*t + 1/2*a*t^2
    d= 0 + 1/2(1.8)(t)^2
    d= 0.9t^2

    Truck:
    d = V * t
    d = 25t


    Put it all together

    0.9t^2 = 25t
    0.9t^2 - 25t = 0


    Now what?
     
  2. jcsd
  3. Oct 10, 2011 #2
    Re: At the instant when the traffic light turns green, a car starts with a constant a

    I think your equation for your truck is wrong. After you have the two equations, put them together and solve for time.
     
  4. Oct 10, 2011 #3
    Re: At the instant when the traffic light turns green, a car starts with a constant a

    How is the truck equation wrong? Please expand
     
  5. Oct 10, 2011 #4
    Re: At the instant when the traffic light turns green, a car starts with a constant a

    In the question, it says that the truck is traveling at a constant velocity of 8.5m/s [F] and in your equation, you have 25 as the velocity.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook