hey everyone i have attached the problems i will try to see what how u guys can solve them and later i will ask questions thanks a lot.
4b) You do this by taking moments of the forces about A.
Let $\displaystyle x$ be the distance of the centre of mass of the plank from A. Then
the sum of the moments of the three forces acting (the weight of the woman,
the weight of the plank and the reaction at B - the reaction at A has zero moment about A so we ignore it) is:
$\displaystyle 2 \times 60 \times g + x \times 90 \times g - 6 \times R_B=0$
where $\displaystyle R_B$ is the reaction at B found in the first part of this question.
RonL