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The Moments of a Springboard

  • Thread starter bobby2000
  • Start date
  • #1
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Homework Statement



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

Homework Equations



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

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!
 

Answers and Replies

  • #2
ehild
Homework Helper
15,406
1,810
(300x2)+(4x400)=RA+(RBx1.6) ---> this is the equation for the torques with respect to A. Why did you include the force RA?

ehild
 
  • #3
2
0
I assumed RA was required for the anticlockwise moment? is it not?
 
  • #4
ehild
Homework Helper
15,406
1,810
RA is force, not torque. What is the torque of RA with respect to A?


ehild
 

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