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Pulley and Mass on an Inclined Ramp

  1. Jun 21, 2009 #1
    1. The problem statement, all variables and given/known data
    A 20 kg mass is released, and the 5 kg mass on the ramp slides up the ramp from rest. As soon as the 5 kg mass gets to the end of the ramp, the string breaks down. What's the tension of the string?

    http://img10.imageshack.us/img10/7603/figure1w.th.jpg [Broken]

    2. Relevant equations
    I would use:
    Fnet = Fg1 + Fg2 + Ff
    Fnet = ma
    Fk = (uk)(Fn)

    The question provies distances too, but I am not sure whether I actually need them...

    3. The attempt at a solution
    First I found the weight of both masses using Fg=mg
    M1(on ramp) = 49N
    M2 (hanging) = 196N

    Then I found the components of Fg (and thus Fn), as shown in my diagram.
    Fn = 42.4N
    Therefore, using Fk = (uk)(Fn), I found the friction to be -11N.

    I know that I have to calculate Fnet. So: Fnet = 196N -24.5N +11N = 182.5N
    *Note: I am not very sure what sign does the friction have in this problem...

    Not sure how to find tension from here... Fnet = Ft + Fgx + Ff?

    Thank you for your time,
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jun 21, 2009 #2

    Doc Al

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    Staff: Mentor

    I recommend that you write separate force equations for each mass, then combine them. For the mass on the incline, consider forces parallel to the incline.
  4. Jun 21, 2009 #3
    Thanks for replying.
    I am not quite sure what you mean by separate force equations for each mass.
    And wouldn't Fgx = 24.5N be the force parallel to the incline?
  5. Jun 21, 2009 #4

    Doc Al

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    Staff: Mentor

    Consider the forces on mass 1. Apply Newton's 2nd law. Do the same for mass 2.
    That's the component of gravity on mass 1 parallel to the incline, but other forces act on that mass.
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