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    dks2114 Posts: 32, Reputation: 2
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    #1

    Oct 8, 2007, 05:32 PM
    Finding distance using Work
    Suppose a gravel ramp slopes upward at 6.0 degrees and the coefficient of friction is 0.40. Use work and energy to find the length of a ramp that will stop a 15000kg truck that enters the ramp at 35 m/s.


    This is what I did:
    I calculated Ff and got 6146.4N. Plugged that into the work formula. Set that equal to KE ((1/2)mv^2 = Fd)and solved for d (and got 1495m). Is this correct?
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    ebaines Posts: 12,131, Reputation: 1307
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    #2

    Oct 9, 2007, 08:49 AM
    I think you're Ff is off - how did you calculate that? Should be Ff = .4 * 15,000kg * 9.8m/s^2 * cos(6 degrees) = 58477 N. Also, don't forget to include the work the truck does against gravity as it rolls up the ramp.
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    dks2114 Posts: 32, Reputation: 2
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    #3

    Oct 9, 2007, 10:12 AM
    Why is it cos(6.0) and not sin(6.0) to find Fn?

    Name: 46.jpg Views: 281 Size: 5.3 KB

    I thought the vector diagram looks like this. Did I put the angle in the wrong place or something?
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    ebaines Posts: 12,131, Reputation: 1307
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    #4

    Oct 9, 2007, 11:57 AM
    The angle you marked in the figure is not 6 degrees: what you marked is the complimentary angle (i.e. 90 - 6 = 84 degrees). Sin(84) and cos(6) are the same.
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    dks2114 Posts: 32, Reputation: 2
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    #5

    Oct 9, 2007, 12:17 PM
    Ohhhh thank you VERY much!
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    ebaines Posts: 12,131, Reputation: 1307
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    #6

    Oct 9, 2007, 01:21 PM
    You're welcome!
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