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    Two forces of magnitude 6N and 5N act on a particle. The angle between the forces is 40 degrees. Find the magnitude and the direction of the resultant force.

    I know you have to use the cosine rule, and in my workinh out I did a^2=b^2+c^2-2bcCosA where cosA is cos40, but the book has cos140 instead. How did they get this?
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    Not too sure if this is right but whenever these Q's come up, the angle I always use is 180 - the stated angle or in this case 140.
    I do it because it always forms the correct triangle.
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    (Original post by _Tyrion)
    Two forces of magnitude 6N and 5N act on a particle. The angle between the forces is 40 degrees. Find the magnitude and the direction of the resultant force.

    I know you have to use the cosine rule, and in my workinh out I did a^2=b^2+c^2-2bcCosA where cosA is cos40, but the book has cos140 instead. How did they get this?
    Getting an answer of 2 degrees for the direction...

    EDIT: 21.86 degrees. I miscalculated
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    Is it because you didn't resolve the forces? Remember you have to form a triangle with the forces placed 'nose-to-tail' before you can solve properly. This might make the difference?
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    (Original post by Sensei_Stig)
    Is it because you didn't resolve the forces? Remember you have to form a triangle with the forces placed 'nose-to-tail' before you can solve properly. This might make the difference?
    Ah good someone knows the official term for my 180 - angle trick.
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    You're welcome! :')
 
 
 
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