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Force and Interaction(Newton) Homework !

  1. Feb 2, 2010 #1
    1. The problem statement, all variables and given/known data

    A man is dragging a trunk up the loading ramp of a mover's truck. The ramp has a slope angle of 20.0°, and the man pulls upward with a force whose direction makes an angle of θ = 26.0° with the ramp.

    (a) How large a force is necessary for the component Fx parallel to the ramp to be 81.0 N?


    (b) How large will the component Fy perpendicular to the ramp then be?


    2. Relevant equations



    3. The attempt at a solution

    SigmaFx=0 becomes F-(Fwsin20degrees)=0
    SigmaFy=0 becomes F-(Fn-Fwcos20degrees)=0

    SigmaFx=F-0.34Fw=0
    SigmaFy=Fn-0.94Fw=0

    I know I need to do force of tension(w/ 26 degrees) + force of gravity (w/ 20 degrees) = 0

    I just cant seem to put it all together.
     
  2. jcsd
  3. Feb 2, 2010 #2
    For part (a) you just need to resolve the forces parallel to the ramp. Draw a diagram of the ramp, the block, and the rope pulling the block. Try answering this... When the angle of the rope is 26 degrees to the plane of the ramp what component (or amount) of the force is going to the task of pulling it along the ramp? And then... if 81N is the force parallel to the ramp what force on the rope is required?

    If this isn't clear, perhaps u could draw a diagram of your resolving of the forces and post it?
     
  4. Feb 2, 2010 #3




    I have made this simple figure for the problem you have .. I hope it will be helpful for you .. if you still have problems ask again ..

    [URL=http://img25.imageshack.us/i/ed96d.jpg/][IMG=http://img25.imageshack.us/img25/8182/ed96d.jpg][/URL][/PLAIN]
     
  5. Feb 2, 2010 #4
    Great guys,thanks so much.
    But one more question , where does the 20 degree angle come into play, could you set up the equations?
    I understand the concept of what I am looking for but setting it up has me stuck.
     
  6. Feb 2, 2010 #5
    i have it set up like the guy did below, but i dont know where to add in 20 degree angle , and whatequations i need to use.
     
  7. Feb 2, 2010 #6
    I dont think that you need the 20 degree angle in your question unless there is a part asking for the normal force for example .. but for the current problem I dont think you need it ..

    and you will just need to use the following equations:

    Fx = F cos(26)
    Fy = F sin(26)

    you have the value for Fx then find F and from there find Fy ..

    Hopefully, that was clear enough for you .. if you have further questions ask ..
     
    Last edited: Feb 2, 2010
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