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Homework Help: Determining reaction forces and angle

  1. Mar 4, 2010 #1
    1. The problem statement, all variables and given/known data
    An assembly is shown in Figure 1, GH, HK and HNL are three cables. The mass of box L is 350 kg,
    a) Determine the mass of box K in order to make angle teta = 30 degrees
    b) Determine the reaction forces at supports G and N.

    i started by converting the 350kg to a force using F=ma, but stuck there...


    digram attached to post

    Attached Files:

  2. jcsd
  3. Mar 4, 2010 #2
    First, do FBD of the pulley that K is on.


    That solves mk.

    Reaction at G is x-component of the above FBD Gx = mLgcos30.

    I'm sure you can figure out Rn now.

    Hope that helps.
  4. Mar 5, 2010 #3
    ye thanks, i think i follow you, but just to clarify,

    FDB is:

    mass of L x gravity x sin30 - mass of K x gravity = 0

    reaction at G:

    G = mass of L x gravity x cos30


    should be:

    y + x values...

    sorry to sound dumb... :(
  5. Mar 6, 2010 #4
    I won't give you the answers, but I'll give you the steps.

    1. Draw FBD of Pulley K
    2. Solve for x and y components to find mass of k and Rg. HINT: the magnitude (or hypotenuse) of the rope that's on 30 deg is the transferred weight of L
    3. Draw FBD of Pulley L. You need a reaction force going up for Rn, and two forces (one on an angle of 30 deg-Also, remember 3rd Law) caused by the weight of Box L.
    4. Split this diagram into x and y components and solve for Rnx and Rny, because the rest is know.

    Do that make sense? Let me know what you get.
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