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Homework Help: Calculating forces

  1. Feb 24, 2014 #1
    1. The problem statement, all variables and given/known data

    two horizontal wire which are separated by 50 degrees are pulling on a 2180 kg mass and cause it to accelerate to the west at 0.25 m/s2. the tension in each rope is 4200.

    a) find the net force on the mass
    b) how much friction is acting on the mass?

    2. Relevant equations

    fnet= ma
    cos law
    sine law

    f = fah-fnet

    3. The attempt at a solution

    so i drew out a free body diagram and calculated the components.
    x1 = cos25 (4200) = 3806 N
    y1 = sin25 (4200) = 1775 N

    x2 = the same as x1
    y2 = the same as y1

    i found fnet by going mass * acceleration and got 545 N

    now calculating friction is difficult. i do not know if i am supposed to use only one x component or both. am i supposed to add 545 or subtract it? all help is appreciated. thanks
    Last edited: Feb 24, 2014
  2. jcsd
  3. Feb 24, 2014 #2


    User Avatar

    Staff: Mentor

    Welcome to the PF.

    Is there a figure/diagram that goes with this question? Can you scan it or copy/paste it as an attachment?
  4. Feb 24, 2014 #3

    this is what i assume the diagram would look like

    the 25 degrees would be the 50 degrees shared by the 2 triangle components

    oh and thanks for the welcome! :)

    Attached Files:

  5. Feb 24, 2014 #4
    Let x be the direction in which the mass is moving. What is the component of force exerted by each of the ropes in the x direction? What is the sum of these two components of force? Write a force balance for the mass in the x direction that includes the two components of rope force, the frictional force, and the mass times acceleration.

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