mxx454
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So for 4a) i took the moment about D rather then A which they did in the mark scheme. I did W X 3.5 + 150x = 100 X 2.5
(i set the distance between the centre and D as x rather then it from A)
I ended up getting 7w + 300x= 500 but it’s supposed to be 550 and i’m not sure where i’ve gone wrong. I should get the same answer despite where i’ve taken the moment from shouldn’t i. Name:  D98BFA86-B578-45DF-B234-E7B1DA283E0B.jpeg
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Last edited by mxx454; 3 weeks ago
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old_engineer
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(Original post by mxx454)
So for 4a) i took the moment about D rather then A which they did in the mark scheme. I did W X 3.5 + 150x = 100 X 2.5
(i set the distance between the centre and D as x rather then it from A)
I ended up getting 7w + 300x= 500 but it’s supposed to be 550 and i’m not sure where i’ve gone wrong. I should get the same answer despite where i’ve taken the moment from shouldn’t i. Name:  D98BFA86-B578-45DF-B234-E7B1DA283E0B.jpeg
Views: 5
Size:  56.4 KB
You can perfectly well take moments about D, but you are not entitled to redefine x, which has been defined for you in the question. The distance from D to the centre of mass of the rod is not x but something else that you can work out quite easily.
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mxx454
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(Original post by old_engineer)
You can perfectly well take moments about D, but you are not entitled to redefine x, which has been defined for you in the question. The distance from D to the centre of mass of the rod is not x but something else that you can work out quite easily.
oh okay thanks
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