Finding the unknown magnitude of force

  1. 1. The problem statement, all variables and given/known data
    Here's a link to the website that has the problem. It's right under example 1.
    http://www.sparknotes.com/testprep/books/sat2/physics/chapter6section3.rhtml


    2. Relevant equations



    3. The attempt at a solution
    This is just for the first part; finding Curly's force.
    For the sled not to move up or down, both Curly and Moe will each have to have a y component force that cancels out the other one. I calculated Moe's y component force to be 17.32 N, which means Curly would also have to have 17.32 N of downward force to negate Moe's force. Then I calculated Curly's x component of force from having his y component of force and got 29.999 N of force.

    What they did is completely foreign to me. First, they got 8.660 N as Moe's y component of force because they multiplied .866, the sine, times the x component. I don't know why they did that.
    Then they just divided the 8.660 they got by Curly's sine to get Curly's x component of force. I don't see why they did that and they don't explain why they were doing it.

    Thanks.
     
  2. jcsd
  3. nrqed

    nrqed 3,054
    Science Advisor
    Homework Helper

    Hi there!

    How did you get that result? The y component cannot be larger than the magnitude, which is 10 N. You have to use

    y component = magnitude times sin(angle measured with respect to the x axis)



    Not quite. They multiplied the sin by the *magnitude* of Moe's force. And that's in agreement with what I wrote above.

    They do not divide 8.660 by any sine. So I am not sure what you are refering to.

    Hope this helps!
     
  4. I assumed the magnitude was their x component force. So their magnitude was the total force they were exerting? Which would be the hypotenuse?
    Oh, ok.
    I was just kinda reading what the last equation was that they did. I'm going to try this again and see if I can do it....


    Ok thanks. I got 17.32 as his force, which is what they got. What confused me is the way they did it at the end. That and I thought the force they were talking about was the force just in the x direction. Don't know why.

    Thanks again.
     
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