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Homework Help: Vector Physics Help

  1. Aug 29, 2007 #1
    Three forces acting upon axis, need to find resultant force and the (equivalent?) force as well.

    2. Frx=84 Grams -> Fry=116 grams up.

    3. I had already found the Resulant X and Y from the three orginal forces (200g @ 20 degrees, 100g at 100 degrees and 100g at 210 degrees) but i am having diffuculty with trying to figure out the direction of the resultant force (I believe the magnittude is ~143g) Its my first assignment in physics and im already lost :[
  2. jcsd
  3. Aug 29, 2007 #2
    use trigonometry.
    tan t = y/x

    edit: you didn't round Fry correctly, it's like .88
    so it should be 117?

    P.S. A nicer way to solve vectors, if they are given like that:
    in calculator (that also shows input on the screen-CASIO fx991)
    store the result in memory,
    and then just change 'cos' to 'sin'

    and now divide this by stored number, and inverse trig would give the theta
    Last edited: Aug 29, 2007
  4. Aug 29, 2007 #3
    o_O I really should blame my geometry teacher but... maybe I should have picked it up myself. Now, y/x gives me ~1.38. Now is there an equation or a function on a calculator that inverses the decimal into a degree? (Sorry if thats what you already mentioned.)

    Possibly something about an inverse tangent?
    Last edited: Aug 29, 2007
  5. Aug 29, 2007 #4
    no i didn't mention it.

    it should be above "tan"
  6. Aug 29, 2007 #5
    I get what you are saying there, thanks for the tip. 117/84 = ~1.39. Now I understand that to be the tangent. I know that all angles have a number to match (such as Sin at 30 degrees is .5) but what I don't know is how to get to .5 to Sin 30 for example.
  7. Aug 29, 2007 #6
    when 0.5 is there on the screen
    press "shift"
    and then sin button
  8. Aug 29, 2007 #7
    ...I am almost too embarrased to say that I was using the Windows calculator. Thanks alot for the help. Im just in 10th grade so all these classes im getting together are getting me flustered. Ill go borrow my friends and continue.
  9. Aug 29, 2007 #8
    o_O for windows, go to view>scientific

    and then select "Inv" option (it's below "Hex" - on the left side of the calculator)
    and then click "sin"
  10. Aug 29, 2007 #9
    Ok I strictly remember doing that and it gave me a smaller decmial. This result (54.2 degrees) is far more logical. Thanks rootX. Used Sin of 54 degrees to confirm that hyp = ~144g and now I know that its at 54 degrees.Adding 180 degrees to hat gives me the Fe of 144g at 234 degrees. ^^ Thanks for the help!
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