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1. Im stuck on question 9 (attached)
For my workings-
80gsin20*2+80gcos20*1= Fsin20*4+Fcos20*2

But this doesn't give the correct answer, which is F= 371N

Thanks
2. (Original post by AvM4N)
Im stuck on question 9 (attached)
For my workings-
80gsin20*2+80gcos20*1= Fsin20*4+Fcos20*2

But this doesn't give the correct answer, which is F= 371N

Thanks
Two things:
For the weight of 80g you should be subtracting the distances.
Also, again for the 80g weight, you've got your sin and cos the wrong way round.
3. (Original post by tiny hobbit)
Two things:
For the weight of 80g you should be subtracting the distances.
Also, again for the 80g weight, you've got your sin and cos the wrong way round.
Thanks! Could you explain why you subtract the distances and why it is 80gcos20*2 and 80gsin20*1because I can't understand why?
4. (Original post by AvM4N)
Thanks! Could you explain why you subtract the distances and why it is 80gcos20*2 and 80gsin20*1because I can't understand why?
Have you drawn a diagram and drawn on the line of action of the weight? Now consider the horizontal distance from A to that line.

5. (Original post by tiny hobbit)
Have you drawn a diagram and drawn on the line of action of the weight? Now consider the horizontal distance from A to that line.
I've attached a picture of my diagram. The arrow points to what I believe would be the force diagram for the weight, but can't see in which corner the 20° angle goes?? Thanks
6. (Original post by AvM4N)

I've attached a picture of my diagram. The arrow points to what I believe would be the force diagram for the weight, but can't see in which corner the 20° angle goes?? Thanks
See if my attachment makes sense.
Attached Files
7. rectangle and moments.doc (32.5 KB, 54 views)

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