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1. The diagram shows a uniform rectangular sign ABCD weighing 50N which is being fixed to a vertical frame. Lengths AD and AB are 120 cm and 80 cm respectively. The corner A is already attached to the frame by a horizontal nail, so that the sign can rotate about A in a vertical plane. While the corner B is being attached an assistant temporarily holds the sign steady at C by a force at 40 degrees to the horizontal. Find the size of this force

Attachment 700400

What I did:

F=39N

But F=14N

2. (Original post by joyoustele)
The diagram shows a uniform rectangular sign ABCD weighing 50N which is being fixed to a vertical frame. Lengths AD and AB are 120 cm and 80 cm respectively. The corner A is already attached to the frame by a horizontal nail, so that the sign can rotate about A in a vertical plane. While the corner B is being attached an assistant temporarily holds the sign steady at C by a force at 40 degrees to the horizontal. Find the size of this force

Attachment 700400

You don't know the magnitude or direction of the force at A , so take moments about A. If you find it easier, split the force at C into vertical and horizontal components before you take moments.
3. (Original post by joyoustele)
RDKGames
What's confusing exactly? Tiny Hobbit has suggested to take moments about A.
4. (Original post by RDKGames)
What's confusing exactly? Tiny Hobbit has suggested to take moments about A.
I did this. I have shown my workings above. Where have I gone wrong?
5. (Original post by joyoustele)
RDKGames Notnek
Please respond to a previous post before tagging someone else.
6. (Original post by joyoustele)
I did this. I have shown my workings above. Where have I gone wrong?
There is also that should be on the LHS. That force also makes the sign go anticlockwise.
7. (Original post by RDKGames)
There is also that should be on the LHS. That force also makes the sign go anticlockwise.
Oh, Thank you. XD. bad mistake from me.

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