# Moments question

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#1
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.
Last edited by mxx454; 3 weeks ago
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3 weeks ago
#2
(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.
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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#3
(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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