1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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


    User Avatar

    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


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Yeah it did go down. Most errors I make are computational rather than systematic.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook