Originally Posted by **Simonamf** Still a little confused if I'm honest.
I appeciate that T = C + H
But I'm not certain how you get to 0.4C = 0.2H and therefore 2C = H
Is it because that as there is no moment around the line at the equal value of the thrust force needs to be applied across H and C and it is split according to the distance from the point at which the force acts against the wall?
Thanks for your help |

OK, to fully understand the mechanics here you have to start off thinking in 3 dimensions.

The gate on face A is in equilibrium and 3D equilibrium requires 6 equations to be satisfied.

3Force equations, one along each axis and 3 Moment equations, one about each axis.

By looking at my first diagram we can quickly reduce this to 2 dimensions.

Now forces act at a point along a line and you can see from my first diagram that the hinge and clasp forces do just this.

But the thrust is distributed across the whole face and acts all along line PQ as shown.

We can replace this by an equivalent force T, acting at the centre of line PQ and develop my second diagram, which the one in part b of your question should look like.

This is 2 dimensional and allows us to write the horizontal and moment equations I have already written, using the information from the first part of your question.

Note we are taking moments about the line PQ so we avoid the question of how the pressure force is distributed along it.

(I assume you ar comfortable with taking moments)

Now I am going to ask you about the third axis because if we take moments about the clasp each hinge force has moment about the third axis through the clasp, so can you write the equilibrium equation for that?