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Homework Help: How long does it take the cars to meet?

  1. Sep 26, 2009 #1
    1. The problem statement, all variables and given/known data
    Two cars are at rest, facing each other, and 300 metres apart.
    If car 1 accelerates at 6.00m/s^2 up to a maximum speed of 30.0m/s and car 2 accelerates at 5.00m/s^2 up to a maximum speed of 35.0m/s, how long does it take the cars to meet?

    2. Relevant equations
    vf= vi + at
    d= (vf + vi/2) * t

    3. The attempt at a solution
    Car 1
    t = 5.00s
    Car 2
    t = 7.00s

    After 5.0s Car 1 has travelled 75m
    After 7.0s Car 2 has travelled 123m

    That's as far as I got...i can't seem to figure out how long it takes for the two cars to meet..help please? I don't know if the numbers i have already are correct or not?
  2. jcsd
  3. Sep 26, 2009 #2


    User Avatar
    Homework Helper
    Gold Member


    Find the equations of motions for both cars. You want the time at which both cars are at the same position x.

    Thus, you have two equations and two variables...
  4. Sep 27, 2009 #3
    Hi, well this is my first time on this site and i came across this question, i'm just about to take my prelim exams and found out i wasn't too sure about this question either...

    This is what i did, if you have the answer say so :P....

    1) Car A did 135 Metres after 7 seconds.
    2) Therefore both cars have done 258 metres altogether after the 7 seconds.
    3) (not sure about this...) Said both cars together are doing 65 metres per second from 7 seconds onwards.
    4) Used the Equations to say that it takes the cars took .69 (to 2 d.p.) seconds to complete the last 42 metres.
    5) Therefore it takes them 7.69 (to 2 d.p.) seconds to meet....

    Not sure if i'm right...
  5. Sep 27, 2009 #4
    The correct answer is 7.65 seconds. So it looks like you're right...
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