Issue with understanding aspects of moments

Dongorgon

Hi all, currently having a few issues with understanding a few aspects of questions involving normal reactions at angles. Just an example of where I am going wrong:

'A loft door OA of weight 100N is propped open at 50 degrees to the horizontal by a strut AB. The door is hinged at O. OA=OB=1m.'

To find the force in the strut, it was fairly straightforward. Taking moments about '0';

0.5x100sin(40)=Fsin(115)

Hence F = 35.46...N

However, when trying to calculate the normal reaction at the hinge, I'm truly lost how to consider the situation?

My attempt leads to: R+(35.46...)cos(25)=100
Which gives R as 67.9 N, yet is a wrong answer?! Any help would be much appreciated, thanks,

tiny-tim

Hi Dongorgon!

You'll need a moments equation.

Choose any point, and take moments about it (the end of the strut would be easiest).