1. Not finding help here? Sign up for a free 30min 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!

Block on an Incline with Varying Elevation

  1. Nov 9, 2011 #1
    The problem statement, all variables and given/known data
    Part one: A block is at rest on an inclined plane whose elevation can be varied. The coefficient of static friction is μs= 0.390, and the coefficient of kinetic friction is μk= 0.190. The angle of elevation θ is increased slowly from the horizontal. At what value of θ does the block begin to slide (in degrees)?

    (Hint after getting it incorrect: mass*acceleration = sum of net forces in one direction. Use mu_s to calculate the frictional force for the moment when it starts to slide)

    Part two: Evaluate the acceleration of the block.



    The attempt at a solution

    So,

    Ff = μFn
    Fn= mgcosθ
    Fparallel = mgsinθ
    Ff = μ(mgcosθ)

    When the block begins to slide, the force of friction has to be equal to the force parallel, right? You have to overcome the static μ.

    So,
    Fparallel = Ff
    mgsinθ = μmgcosθ

    mg's would cancel, so

    sinθ = μcosθ
    sinθ/cosθ = μ
    tanθ = μ

    θ= tan^-1(0.390)

    However, the answer I get is 0.372°, and that isn't correct.

    For the second half,
    ƩFnet = ma
    Fparallel - Ff = ma
    mgsinθ - mgcosθ = ma
    gsinθ - gcosθ = a


    There's a flaw in my method, I just don't know what it is. Anyone know how to help?
     
  2. jcsd
  3. Nov 9, 2011 #2
    Your answer was right. It's just that you are in radians, rather than degrees.
     
  4. Nov 9, 2011 #3
    Thank you. I feel like a bit of an idiot, but I guess that's what I get for working with a new calculator.

    Thank you!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Block on an Incline with Varying Elevation
  1. Block on Incline (Replies: 1)

  2. Blocks on Incline (Replies: 1)

  3. Blocks on an Incline (Replies: 37)

  4. Block on Incline (Replies: 3)

Loading...