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Math Help - Resolving forces

  1. #1
    Junior Member
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    Resolving forces

    Hey guys,
    Question: A mass of 2.6 kg is maintained in equilibrium in a vertical plane by forces of 5P N and 12P N (where P is an unknown constant) which are perpendicular.
    5P is at an angle \alpha from the vertical.
    Find the value of \alpha and the value of the constant P.

    So 12p is at an angle of 90-\alpha  from the vertical. (My reasoning)

    Resolving vertically I get: 5p\cos \alpha + 12p\sin \alpha =26
    And horizontally: 12p\cos \alpha = 5p\sin \alpha

    After that I'm stuck, simultaneous equations I presume.
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  2. #2
    Senior Member abhishekkgp's Avatar
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    Quote Originally Posted by elieh View Post
    Hey guys,
    Question: A mass of 2.6 kg is maintained in equilibrium in a vertical plane by forces of 5P N and 12P N (where P is an unknown constant) which are perpendicular.
    5P is at an angle \alpha from the vertical.
    Find the value of \alpha and the value of the constant P.

    So 12p is at an angle of 90-\alpha  from the vertical. (My reasoning)

    Resolving vertically I get: 5p\cos \alpha + 12p\sin \alpha =26
    And horizontally: 12p\cos \alpha = 5p\sin \alpha

    After that I'm stuck, simultaneous equations I presume.
    from the second equation you get the value of \tan \alpha =12/5. hence \sin \alpha=12/13 and \cos \alpha = 5/13 (why?).
    substitute in above.
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  3. #3
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    didn't see that!
    Thank you!
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