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I Question about Resultant Forces

  1. Oct 24, 2016 #1

    Alright, so after looking at this video to do it

    I did the following.

    F1(65N) = 65cos(30)i+65sin30i

    Then using the radian circle I saw that 30* has x,y coordinates of sqrt3/2 and 1/2 respectively. So as shown in the video I did


    = 56.3i + 32.5j

    I did this for the left one too (30N).

    But for the one at the bottom (20N) I get the degree of it to be 250. (270-20) = 250.

    250* is not on the radian circle so how can I write 250* in terms of x,y coordinates?

    Thanks in advance.
  2. jcsd
  3. Oct 24, 2016 #2


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    Hello Pablo, :welcome:

    Please post in the homework forum (and make good use of the template there!)

    180-20 = 250 seems strange to me. But 270 - 20 - 250 and that's the right angle. Why do you say it's not on the radian circle ? Does that go from ##-\pi## to ##+ \pi## ? If so, how far from 0 to 270 when starting at 0 ?
  4. Oct 24, 2016 #3
    Oh ya I wrote it wrong, I meant to write 270-20 = 250.

    But if we look at this radian circle. We see that 240* = (-1/2, -sqrt3/2) and then it goes to 270* = (0,-1). How can I find the x,y coordinates for 250* and use it in the equation?

    And sorry about posting in the wrong section, I'll fix it next time. Do I need to repost this to the homework section or is it fine?
  5. Oct 24, 2016 #4


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    I see. 250 degrees isn't in the list. Calculators (or spreadsheets) not allowed ? You need ##\ \cos 250^\circ\ ## and ##\ \sin 250^\circ##

    Thread will be moved by a moderator, don't worry.
  6. Oct 24, 2016 #5
    Oh my bad I posted it over there already. I 'll see if I can delete it.

    Ya we can use calculators but maybe Im doing it wrong. Should it be in degrees or radians?

    Ooh, I can just do it on my calculator? I assumed you'd have to use the radian circle. Well... I feel dumb. Thanks a lot though :)

    And I already posted it to the homework section again but I'll post that it's been solved. Thanks again.
  7. Oct 24, 2016 #6


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    When in radians mode your angle is ##250^\circ \displaystyle {\pi\over 180^\circ}##

    -- lots of people blindly type in an angle in the wrong mode and end up with nonsense (and marks lost), so be warned.
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