1. Not finding help here? Sign up for a free 30min 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!

Quick algebra based question

  1. Sep 6, 2006 #1
    Train leaves station going 50MPH
    Car leaves station going 70MPH - 2 hours later

    How far til car catches train?

    This should be so simple, here is what I've done:



    I get t=7 miles for my final answer, but according to the book this is wrong. Why?
  2. jcsd
  3. Sep 6, 2006 #2
    try it this way: when the car starts the train is 100 miles away. the car makes up ground at 20 miles/hour (70-50)... how many hours does it take to catch the train... how many miles did the car go in that time.
  4. Sep 6, 2006 #3
    How did you get miles from that? If
    d=50mph*t hours

    50mph*t hours=70mph*(t-2)hours
    50mph*t hours=70mph*t hours-140 miles
    140 miles=20mph*t hours
    140miles/20mph = t hours
    7 hours = t hours
  5. Sep 6, 2006 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I think the problem is that you've solved for t when the question asks you to solve for d, the distance.

    Of course you can now just put t back into one of the equations.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Quick algebra based question
  1. Quick algebra pointer (Replies: 4)