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Homework Help: Bar of soap

  1. Oct 3, 2004 #1
    A wet bar of soap slides freely down a ramp 9.35 m long inclined at 7.00°. How long does it take to reach the bottom? Assume muk = 0.0550.

    Okay I've got my x & y componants
    9.35cos(7)=9.28
    9.35sin(7)=1.14

    But now what since I don't have the mass of the soap or the acceleration, what do I do next?
     
  2. jcsd
  3. Oct 3, 2004 #2
    Draw yourself a free-body diagram of the situation. It should be pretty clear to you from then on.
     
  4. Oct 3, 2004 #3
    Okay I drew my FBD but I still don't know how much time it would take the soap to slide down the ramp. Maybe I'm missing something.
    I have the frictional force going NW the normal force going NE and the weight force going South... is that right?
     
  5. Oct 3, 2004 #4
    Yes. Set up the equations using Newton's 2. law, solve for the acceleration and use some kinematics to solve for time.
     
  6. Oct 3, 2004 #5
    How do I solve for acceleration if the mass is unknown?
     
  7. Oct 3, 2004 #6

    arildno

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    Well, but since the frictional force, the gravity and the "ma" terms are all proportional to the mass, it's a common factor which you can eliminate
    (the solution is independent of the mass)
     
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