# The Moments of a Springboard

## 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!

ehild
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

I assumed RA was required for the anticlockwise moment? is it not?

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

ehild