1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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: Motion problem for constant acceleration of truck

  1. Sep 20, 2010 #1
    1. The problem statement, all variables and given/known data
    A truck travels at a constant speed of 28.0 m/s in the fast lane of a two-lane highway. It approaches a stationary car stopped a the side of the road. When the truck is still 125 m behind the car, the car pulls out into the slow lane with an acceleration of 2.6 m/s2. How long will it take the truck to reach the car? (Answer is 6.32 s)

    2. Relevant equations
    dt = dc + 125
    dc = 1.3t2

    3. The attempt at a solution
    Okay I got the answer, but it's in quadratic form so:

    1.3t2 - 28.0t + 125 =

    t = 15.2 s or t = 6.32 s

    How do you know which answer is the correct one?
  2. jcsd
  3. Sep 20, 2010 #2
    Hello? Please, I need help :frown:
  4. Sep 21, 2010 #3
    How did you come up with your equation? You must have started from the basic kinematic equations, right?

    Go back to those and try both values of t to see which one works/makes more sense.
  5. Sep 21, 2010 #4
    Think about what this means...

    At the end of t=6.32s, how fast is each vehicle moving (what are their velocities)?
    What is the distance covered by each in this time interval?

    What about at t=15.2s?
  6. Sep 21, 2010 #5
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook