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Homework Help: Block on incline

  1. May 17, 2016 #1
    1. The problem statement, all variables and given/known data
    3.00-kg block starts from rest at the top of a 30.0° incline and slides a distance of 2.00 m down the incline in 1.50 s. Find (a) the magnitude of the acceler- ation of the block, (b) the coefficient of kinetic friction between block and plane, (c) the friction force acting on the block, and (d) the speed of the block after it has slid 2.00 m.

    2. Relevant equations

    3. The attempt at a solution
    a = 1.78 m.s2

    (B) fk - mgsin@ = ma
    Ukmgcos@ - mgsin@ = ma
    Ukgcos@ -gsin@ = a
    Uk= (a+ gsin@)/gcos@
    Uk = 0.787
  2. jcsd
  3. May 17, 2016 #2
    Not getting the correct answer where am I going wrong?
  4. May 17, 2016 #3


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    Staff: Mentor

    You have a sign issue with the directions of the vector components. Draw an FBD that shows the directions of the vectors involved. Include the acceleration vector so that your choice of coordinate system is clear (so that the signs you assign to the force vectors when you write your equations match your choice of + direction for the acceleration).
  5. May 18, 2016 #4
    Oh yes its suppost to be mgsin@ -fk
  6. May 18, 2016 #5
    But i still get the same eqn
  7. May 18, 2016 #6


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    Homework Helper
    Gold Member

    Signs should change in your equation.
  8. May 18, 2016 #7
    Ya I see it now. I made such a stupid mistake
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