MHB Statics for rod attached to string

[markosheehan]

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could someone please explain to me why there is no relative force at point a where the rod ab is attached to a

thanks

 

[I like Serena]

could someone please explain to me why there is no relative force at point a where the rod ab is attached to a

thanks

There is.
In the answer key it has been left out, since it's focusing on the moments about a.
The force at point a does not contribute to the moments about a.

 

[markosheehan]

thanks

I do not see how they can just resolve forces at point c horizontally and vertically. For these type of questions I was always told you can only resolve forces horizontally and vertically for the whole system not just 1 random point on the system. can you just resolve forces horizontally and vertically for 1 point on all types of questions like these.

I can also not see why/how they can take moments about point b for just point c. again I was always told when taking moments about a point you have to take all forces in the whole system about point c not just the forces at one point in the system.