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Homework Help: Only girl on electro engineering

  1. Mar 11, 2009 #1
    Only girl on electro engineering :(

    Hello! This is my first post but not the last! :D
    I'm a student at norwegian universety and I really have difficulty with phisics

    Here's my question (look at attacment)

    How big force F has to be so that B doestn't change position (doesn't flys over and doesn't fells down)?

    Answer is this:

    Mg(tanø*y) Mg(tanø+ y)
    ------------ < F< -----------
    1+y*tanø 1-y*tanø

    y=friction ( between A and B)

    I'm not very proud to say that I used 10 hours in the row on this, so any help will be very appreciated!

    Attached Files:

  2. jcsd
  3. Mar 11, 2009 #2


    User Avatar
    Homework Helper

    Re: Only girl on electro engineering :(

    Welcome to PF.

    Consider then the forces acting on the block A, with mass call it m, along the plane of the incline.
    Gravity wants it to slide down at m*g*sinθ
    Friction wants to hold it at μ*m*g*cosθ

    Now what about your force F ?

    How much is it accelerating the system of A and B?

    Then what components of that force are increasing friction? and what component is wanting to push it up the incline?
  4. Mar 28, 2009 #3
    Re: Only girl on electro engineering :(

    Hi! I am a newcomer too... So welcome:P
    Where is the Force apllied? To the A body? To the B? To none of these?
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