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# M3 OCR : Systems of Rigid Objects Question 5 Watch

1. I have resolved in both directions for AC and BC to get all the horizontal components are equal and have also got expressions for the vertical components.

Here is the question:

Two fixed points A and B on a horizontal beam are 4metres apart. Two rods AC and BC, of length 5m and 3m and weight 100N and 60N, are connected to each other by a pin joint at C, and to the beam by pins at A and B. find the forces on the rods from the pins at A,B and C.

Thanks for the help
2. (Original post by HashBrowns)
I have resolved in both directions for AC and BC to get all the horizontal components are equal and have also got expressions for the vertical components.
Good, but what are they? And is C above or below the line AB?

Also, if you have the solutions, it would be a helpful.
3. C is below the line AB, and Y at A = 160- Y at B, Y at C = 60 - Y at B.

On AC: 50N upwards at A, 50 N upwards at C
On BC: 110 N upwards at B, 50N downward at C
4. (Original post by ghostwalker)
Good, but what are they? And is C above or below the line AB?

Also, if you have the solutions, it would be a helpful.
Please see above - sorry forgot to quote you earlier!
5. (Original post by HashBrowns)
C is below the line AB, and Y at A = 160- Y at B, Y at C = 60 - Y at B.

On AC: 50N upwards at A, 50 N upwards at C
On BC: 110 N upwards at B, 50N downward at C
Y at A and Y at B are both upwards, Y at C will depend on which rod you're referencing, as to whether it's up or down.

You should notice that you have a 3,4,5 triangle, and so the rod BC is vertical.

If you take moments about A for the rod AC, then Y at C drops out straight away, and the rest should follow.
6. Thanks I solved it.
7. (Original post by HashBrowns)
Thanks I solved it.
Good.

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