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Homework Help: Finding Friction Coefficient

  1. Mar 7, 2006 #1
    Here it is.
    A 10 kg suitcase is placed on a flat ramp inclined at 37 deg. When released from rest, the suitcase accelerates down the ramp at .15 m/s^2. What is the coefficient of the kinetic friction between the suitcase and the ramp?

    Now, from this I got Fnet=m*a=1.5 N in the x direction.

    Fnet=Fx-kinetic friction=mg(sin theta)-mg(cos theta)(mu k)
    solving for mu k:
    mu k=mg(sin theta)-Fnet)/mg(cos theta)

    Doing all the math gets me something like .46, but the back of the book disagrees. What am I doing wrong?
  2. jcsd
  3. Mar 7, 2006 #2
    The question is wrong. The acceleration is greater than g.
  4. Mar 7, 2006 #3
    It's 0.15 m/s^2. I left out the 0, so it might've looked like 15. Sorry.
  5. Mar 7, 2006 #4


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    Staff Emeritus
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    I can't see that you've done anything wrong.
  6. Mar 7, 2006 #5
    The answer I get is .468, but the book gives .73. Unless the book is wrong, which I guess is conceivable.
  7. Mar 7, 2006 #6


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    Staff: Mentor

    I set it up the same way and got u=0.734. Maybe just re-check your math after the last equation.
  8. Mar 7, 2006 #7
    Show your calculations.
  9. Mar 8, 2006 #8
    Thanks, I got it. I had forgotten to add a parenthesis when putting it into my calculator. Stupid me. I tried to post this yesterday, but the forum seemed to go down.
  10. Mar 8, 2006 #9


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    Yeah it did go down. Most errors I make are computational rather than systematic.
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