Finding Friction Coefficient

  • Thread starter superdave
  • Start date
  • #1
150
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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?
 

Answers and Replies

  • #2
335
0
The question is wrong. The acceleration is greater than g.
 
  • #3
150
3
It's 0.15 m/s^2. I left out the 0, so it might've looked like 15. Sorry.
 
  • #4
Hootenanny
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I can't see that you've done anything wrong.
 
  • #5
150
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The answer I get is .468, but the book gives .73. Unless the book is wrong, which I guess is conceivable.
 
  • #6
berkeman
Mentor
60,422
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I set it up the same way and got u=0.734. Maybe just re-check your math after the last equation.
 
  • #7
335
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Show your calculations.
 
  • #8
150
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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.
 
  • #9
Hootenanny
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Yeah it did go down. Most errors I make are computational rather than systematic.
 

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