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: Confusing Physics Question

  1. Feb 27, 2005 #1
    Just looking over some extra physics questions and I came upon this one, it seems quite easy, but difficult when i actually attempted it:
    Just as a traffic light turns green, a waiting car starts off with a constant acceleration of 6.00m/s^2. At the instant the car begins to accelerate, a truck with a constant velocity of 21.0m/s passes in the next lane. How far will the car travel before it overtakes the truck? How fast will the car be travelling when it overtakes the truck?
    I attempted this question by changing the car's acceleration to a velocity by multiplying with an amount of time, etc.
    I imagine that this question could possibly be done with trial and error,but i'm just wondering if there's a quicker way to attempt this question or a specific formula. Any hints or pointers, plz post!
     
  2. jcsd
  3. Feb 27, 2005 #2
    problem solved!

    I have solved this question, therefore i am no longer using this thread. If there is anyone who wishes to post here, by all means go ahead! :smile:
    Thx,
    jen333

    ps) for those who would like to know, the answer is 24m/s.
     
  4. Mar 1, 2005 #3
    It has been a while, so maybe I am wrong, but this is what I got:
    [tex]0.5at^2=21t[/tex]
    [tex]3t^2=21t[/tex]
    [tex]t^2=7t[/tex]
    [tex]t={0, 7}[/tex]

    therefore:
    [tex]v=ta[/tex]
    [tex]v=42[/tex]
     
    Last edited: Mar 1, 2005
  5. Mar 1, 2005 #4

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    Yes,the velocity is 42m/s...It's correct.And the distance is 147m...

    Daniel.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook