1. Limited time only! Sign up for a free 30min personal 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!

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...

    help

    digram attached to post
     

    Attached Files:

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

    [tex]\Sigma[/tex]Fy=0=mLgsin30-mkg

    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

    Rn:

    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.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook