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# Moments help.... watch

1. Steeple jack rides on a beam,The mass of the beam and the mass of the steeple jack is 2000kg and 80kg, respectively, the length of the beam is 12m, and chains hang vertically, from the crane, one chain 10m from the left end, and second chain on the very end of the left end. The steeple jack sits at a distance of 7m from the left end. Find the tension in each of the chains. (Beam is horizontal and at rest)

my working:

have i done anything wrong?

Diagram:
Attachment 698356
2. yoi should have multiplied the mass times 9.8 to get the weight in newtons
3. (Original post by joyoustele)
Steeple jack rides on a beam,The mass of the beam and the mass of the steeple jack is 2000kg and 80kg, respectively, the length of the beam is 12m, and chains hang vertically, from the crane, one chain 10m from the left end, and second chain on the very end of the left end. The steeple jack sits at a distance of 7m from the left end. Find the tension in each of the chains. (Beam is horizontal and at rest)

my working:

have i done anything wrong?

Diagram:
Attachment 698356
I assume you took the chain to the right as the pivot? In which case, the centre of mass of the beam is 4 away from the the pivot, not 5. I assume the beam is uniform.
4. (Original post by olive green)
yoi should have multiplied the mass times 9.8 to get the weight in newtons
i tried it, it didnt work
5. (Original post by RDKGames)
I assume you took the chain to the right as the pivot? In which case, the centre of mass of the beam is 4 away from the the pivot, not 5. I assume the beam is uniform.
it doesnt say it is in uniform.
6. (Original post by joyoustele)
it doesnt say it is in uniform.
Then where is it's centre of mass?
7. (Original post by RDKGames)
Then where is it's centre of mass?
They didnt say it was in uniform, but i think we had to assume it was, as using 4 instead of 5, i managed to get the correct answer.

Why is it 4 though? Thats the bit i struggle with.
8. (Original post by joyoustele)
They didnt say it was in uniform, but i think we had to assume it was, as using 4 instead of 5, i managed to get the correct answer.

Why is it 4 though? Thats the bit i struggle with.
The length is 12m, so COM is halfway there which makes the distance from the right end 6m. Distance from COM to right chain = a m, so distance from right chain to left end is 2m, hence 4+a=6 and so a=4
9. (Original post by RDKGames)
The length is 12, so COM is halfway there which makes the distance from the right end 6. Distance from COM to right chain = a, so distance from right chain to left end is 2, hence 4+a=6 and so a=4
oh yh, hhhhhhhhhhhhh, Thanks

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