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Math Help - [Kinematics] Faster way?

  1. #1
    Junior Member Cthul's Avatar
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    [Kinematics] Faster way?


    I know how to do it, but it's ridiculously long.
    How do I do this the fast way, assuming there is one.
    I found the area of all and removed the negative areas to get the distance.

    \frac{\text{distance}}{\text{time}}

    And correctly got A.
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  2. #2
    MHF Contributor undefined's Avatar
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    Quote Originally Posted by Cthul View Post
    I know how to do it, but it's ridiculously long.
    How do I do this the fast way, assuming there is one.
    I found the area of all and removed the negative areas to get the distance.

    \frac{\text{distance}}{\text{time}}

    And correctly got A.
    I don't think there's a faster way with the information you've been given. You just have to be fast with finding areas of triangles and rectangles (and trapezoid/trapezium) and seeing when certain things cancel each other out.

    Now, if you'd been given the start position (call it a) and end position (call it b), then there would be an easier way. It would be (1/14)(b-a). (By the fundamental theorem of calculus.)

    Edit: You could however eliminate B immediately, since there's no way a denominator of 14 could get simplified to 16. You could eliminate E by eyeballing it. But I don't see easy ways to eliminate C and D.
    Last edited by undefined; June 1st 2010 at 10:56 PM.
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  3. #3
    Junior Member Cthul's Avatar
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    Quote Originally Posted by undefined View Post
    I don't think there's a faster way with the information you've been given. You just have to be fast with finding areas of triangles and rectangles (and trapezoid/trapezium) and seeing when certain things cancel each other out.

    Now, if you'd been given the start position (call it a) and end position (call it b), then there would be an easier way. It would be (1/14)(b-a). (By the fundamental theorem of calculus.)

    Edit: You could however eliminate B immediately, since there's no way a denominator of 14 could get simplified to 16. You could eliminate E by eyeballing it. But I don't see easy ways to eliminate C and D.
    Could you show me how you would do it?
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  4. #4
    MHF Contributor undefined's Avatar
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    Quote Originally Posted by Cthul View Post
    Could you show me how you would do it?
    No problem.

    So going from point A to B, the area is 0 because the positive and negative contributions are equal.

    Then from B to C it's -18.

    Then from C to the place where it crosses the x-axis, it's -6, making overall total of -24. Then from that point to D it's 24, making overall total 0.

    Then from D to E it's 2 * (average of 8 and 12) = 20. So the answer is 20/14 = 10/7.
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  5. #5
    Junior Member Cthul's Avatar
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    Thanks, that's really helpful. I wasn't aware of the first part being that they would cancel out.
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