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Math Help - quadratic

  1. #1
    Member smmmc's Avatar
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    quadratic

    hi, need help

    A window washer drops a squeegee from a scaffold 100 m off the ground. The
    relationship between the height of the squeegee (h), in metres, and the length of time
    it has been falling (t), in seconds, is given by h = 100 − 5t2.
    a) When does the squeegee pass a window 30 m off the ground?
    b) How long does it take for the squeegee to hit the ground?

    thanks!
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  2. #2
    Like a stone-audioslave ADARSH's Avatar
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    Quote Originally Posted by smmmc View Post
    hi, need help

    A window washer drops a squeegee from a scaffold 100 m off the ground. The
    relationship between the height of the squeegee (h), in metres, and the length of time
    it has been falling (t), in seconds, is given by h = 100 − 5t^2.
    a) When does the squeegee pass a window 30 m off the ground?
    b) How long does it take for the squeegee to hit the ground?

    thanks!
    For squeegee to be 30 metres above the ground

     <br />
h = 30 = 100- 5t^2<br />

    Hence
    70= 5t^2

    Thus t^2 = 14
    Hence t = \pm \sqrt{14}
    Since time cannot be negative its taken as t= \sqrt{14} s


    For squeegee to hit the ground its height should be 0
    so
    h= 0 = 100- 5t^2

    Thus
    5t^2 = 100

    Hence
    t^2 = 20

    Hence
    t= \sqrt {20}s = 2\sqrt{5}s
    Last edited by ADARSH; February 24th 2009 at 02:05 AM. Reason: BECAUSE I DID IT WRONG
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  3. #3
    Member smmmc's Avatar
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    Quote Originally Posted by ADARSH View Post
    For squeegee to be 30 metres above the ground

     <br />
h = 30 = 100- 5t^2<br />

    Hence
    20= 5t^2

    Thus t^2 = 4
    Hence t = \pm 2
    Since time cannot be negative its taken as t= 2s


    For squeegee to hit the ground its height should be 0
    so
    h= 0 = 100- 5t^2

    Thus
    5t^2 = 100

    Hence
    t^2 = 20

    Hence
    t= \sqrt {20}s = 2\sqrt{5}s
    hey how did you get the 20 in this 20= 5t^2
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  4. #4
    Like a stone-audioslave ADARSH's Avatar
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    Quote Originally Posted by smmmc View Post
    hey how did you get the 20 in this 20= 5t^2
    By mistake
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