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Homework Help: Calculation Error?

  1. Nov 13, 2004 #1

    I'm in the middle of a problem on the online program Webassign, trying to calculate the coefficient of friction in a problem. I have the correct value of the force of friction, and I believe I have the correct Normal Force value, but the program is rejecting my answer.

    The problem involved a 21kg box sliding down a 38 degree inclined plane at an acceleration .270 m/s^2, and I calculated the force of friction to be 121.033N. To solve for the coefficient of friction I am using the equation Ff=uFn → u=Ff/Fn= 121.033N/205.8N=.588

    Did I make an error or is it a glitch in the program?
  2. jcsd
  3. Nov 13, 2004 #2


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    Dearly Missed

    Your normal force is incorrect, it seems.
    If you used N=mg, that's where your mistake lies.
  4. Nov 13, 2004 #3
    ooh yikes, thank you, I didn't notice that. And I drew the vector diagram too, so I should've realized lol. Thank you!
  5. Nov 13, 2004 #4
    Use g as 9.81m/s^2 and not 9.8m/s^2 and you might get the right answer
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