1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    User Avatar
    Homework Helper

    (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

    User Avatar
    Homework Helper

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


    ehild
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook