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Math Help - How to find the velocity of the train using the graph below?

  1. #1
    Junior Member silvercats's Avatar
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    How to find the velocity of the train using the graph below?

    http://oi52.tinypic.com/1zg7oxy.jpg


    I got few equations but not correct I guess
    (1/2)v(60+60-(t1+t3))=432

    1/3=v/t1
    and 1=v/t3

    after manipulating the answers I get a way off answer which is not even close to the answer in the book.explained details are appreciated
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  2. #2
    MHF Contributor alexmahone's Avatar
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    Quote Originally Posted by silvercats View Post
    http://oi52.tinypic.com/1zg7oxy.jpg


    I got few equations but not correct I guess
    (1/2)v(60+60-(t1+t3))=432

    1/3=v/t1
    and 1=v/t3

    after manipulating the answers I get a way off answer which is not even close to the answer in the book.explained details are appreciated
    Your method seems right.

    \frac{1}{2}(120-3v-v)=432

    v(60-2v)=432

    30v-v^2=216

    v^2-30v+216=0

    (v-18)(v-12)=0

    v=18\ or\ 12

    But v=18 \implies t_1=54\ and\ t_3=18 (Contradiction since the times add up to more than 60.)

    Therefore, v=12
    Last edited by alexmahone; May 15th 2011 at 07:21 AM.
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  3. #3
    Junior Member silvercats's Avatar
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    That is great.thanks!
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