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Issue with understanding aspects of moments

  1. Mar 16, 2013 #1
    Hi all, currently having a few issues with understanding a few aspects of questions involving normal reactions at angles. Just an example of where I am going wrong:

    'A loft door OA of weight 100N is propped open at 50 degrees to the horizontal by a strut AB. The door is hinged at O. OA=OB=1m.'

    To find the force in the strut, it was fairly straightforward. Taking moments about '0';

    0.5x100sin(40)=Fsin(115)

    Hence F = 35.46...N

    However, when trying to calculate the normal reaction at the hinge, I'm truly lost how to consider the situation?

    My attempt leads to: R+(35.46...)cos(25)=100
    Which gives R as 67.9 N, yet is a wrong answer?! Any help would be much appreciated, thanks,
     
  2. jcsd
  3. Mar 16, 2013 #2

    tiny-tim

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    Hi Dongorgon! :smile:

    You'll need a moments equation.

    Choose any point, and take moments about it (the end of the strut would be easiest). :wink:
     
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