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Homework Help: The Moments of a Springboard

  1. Mar 5, 2010 #1
    1. The problem statement, all variables and given/known data

    The diagram (not included) shows a straight, horizontal swimming bath spring board of length 4m and weight 300N. It is freely hinged at A and rests on a roller at B where AB=1.6m. A boy of weight 400N standard at end C.
    a) show directions of forces acting on A and B
    b) calculate magnitudes of forces at A and at B

    2. Relevant equations

    A______________B______________C
    AB= 1.6m
    BC= 2.4m
    AC= 4m

    3. The attempt at a solution
    Weight of board put at centre point (0.4m from B and 2m from C)
    RA assigned as reaction force at A
    RB assigned as reaction force at B

    RA = 700-RB

    RA+RB = 700N
    (300x2)+(4x400)=RA+(RBx1.6)
    2200=RA+(RBx1.6)
    2200=700-RB+(RBx1.6)
    1500=0.6RB
    2500=RB

    This figure for RB simply cannot be right and therefore really isn't helping me!
     
  2. jcsd
  3. Mar 5, 2010 #2

    ehild

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    (300x2)+(4x400)=RA+(RBx1.6) ---> this is the equation for the torques with respect to A. Why did you include the force RA?

    ehild
     
  4. Mar 5, 2010 #3
    I assumed RA was required for the anticlockwise moment? is it not?
     
  5. Mar 5, 2010 #4

    ehild

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    Homework Helper

    RA is force, not torque. What is the torque of RA with respect to A?


    ehild
     
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