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!

Moving Wedges

  1. Mar 6, 2007 #1
    1. The problem statement, all variables and given/known data
    A wedge of mass 4kg and angle 30 degrees is at rest on a smooth horizontal table. a mass of 1kg is placed on the smooth inclined face of the wedge and a horizontal force of 10N is applied to towards the vertical face of the wedge. Show that the acceleration of the wedge is

    (40 - root(3g) ) / 17 ~= 1.35m/s.


    Also find the reaction force between the wedge and the mass


    2. Relevant equations



    3. The attempt at a solution

    (from diagrams)

    Equation of wedge horizontally

    4A = 10 - Rsin30 (1)

    Equation of mass horizontally


    A + acos30 = Rsin30
    A = Rsin30 - acos30 (2)



    Equation of mass vertically

    asin30 = g - Rcos30 (3)


    Substitute (2) into (1)

    4(Rsin30 - acos30) = 10 - Rsin30
    5Rsin30 - 4acos30 = 10
    5Rsin30 = 10 + 4acos30
    5R* 1/2 = 4a * root(3)/2 + 10
    5R/2 = 2 root(3)a + 10
    5R = 4root(3)a + 20
    R = ((4root(3)a) / 5) + 4

    Now I have 'R' in terms of 'a', but I'm not sure where to go. My notes on this trail off...I seem to substitute R back into equation (1), along with equation (2) but that will just give me R in terms of a again.
     

    Attached Files:

  2. jcsd
  3. Mar 6, 2007 #2
    it seems you missed a equation.

    you can achieve a=2g-root(3)R from
    asin30 = g - Rcos30 (3)

    then subtitute it to
    5R = 4root(3)a + 20
    it can give you R without a

    besides, i really cann't understand then method you used in this problem and so as what the A stand for.i suggest you consider more ways.
     
  4. Mar 7, 2007 #3
    where does the 'missing equation' come from?
    I can't actually recall why A is there, though I'm sure i need it :/ could it be the force of the mass pushing the wedge back?
     
  5. Mar 7, 2007 #4
    :tongue:

    you missed equation (3)

    just tell me what the A stand for in the picture in order to let me understand it in your way.
     
  6. Mar 8, 2007 #5
    sorry for the delay in replying.

    A represents the acceleration of the wedge.
     
  7. Mar 17, 2007 #6
    really sorry for so many days' delay.

    in my peasonal sense,non-inertial frame will greatly predigest the problem.just use the wedge as frame.
    in addition,you missed a force on wedge in the maps you gave.

    happy new day!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Moving Wedges
  1. Moving Wedge (Replies: 6)

Loading...