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AS Physics Moments Question

  1. Aug 19, 2011 #1
    1. The problem statement, all variables and given/known data
    Was doing some past papers in preparation for mock Cambridge exams when I ran into this question. Image should be on here I hope...


    2. Relevant equations
    Moment=Force x Perpendicular distance from pivot point?


    3. The attempt at a solution
    Dunno how to start this one, anyone that can point me in the right direction will be much appreciated!
     

    Attached Files:

  2. jcsd
  3. Aug 19, 2011 #2

    rock.freak667

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    Homework Helper

    Yes, this is all you need

    Well firstly start by taking clockwise moments as positive (or negative, it doesn't really matter)

    So which forces would cause a clockwise moments and what are these moments equal to? (write them separately and then add them; also remember your convention so these are positive; negative if you chose otherwise )

    Similarly, which forces cause anticlockwise moments, write them down with the appropriate sign?


    If you are having trouble with finding the distances, draw a vertical line and horizontal line through P, then for each for each force's direction draw a perpendicular line to it until it intersects with your line through P, this will the perpendicular distance. (Say if the force is vertical, you would draw a horizontal line)
     
    Last edited: Aug 20, 2011
  4. Aug 19, 2011 #3
    Using positive moments as clockwise rotation, The 20N force x 3m distance makes 60Nm. Then with the 5N and 10N forces become -10Nm and -20Nm respectively. 60-20-10= 30Nm which was the correct answer. Thanks heaps!
     
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