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# help mechanics 1 question moments watch

1. hey..the question says "a uniform plank AB of length 5m and mass 30 kg is resting horizontally on supports C and D where AC=1m and AD =3.5 m. When a particle of mass 14kg is attached to the rod at point E the magnitude of the reaction at C is equal to the magnitude of the reaction at D. Find the distance AE.

okay so i know the formula of answering such questions but the problem here is that..i don't know where to include the point E in diagram so i can calculate. Like how will I know if E is before or after C?Or is it before D or after D? Is there a way i can figure that out?
2. It isn't essential to get E in exactly the right place (although you can often reason this out), but you do have to get it the right side of the point that you are taking moments about. Which point have you decided to take moments about?
3. how will I equate clockwise and anticlockwise moments without knowing the position? like how can i know whether it's before or after C...or before D or after D? here is my diagram (without E)
4. It's pretty unlikely that it will be to the left of C. Put it anywhere to the right of C, and if you take moments about C, it will be a clockwise moment. These things tend to get sorted out by the algebra - if you make the wrong choice, you often get a negative answer which corresponds to having chosen the wrong side.
5. ahh yes that makes sense now..thank you very much! Really appreciate

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