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"That their main business was not put into the mind knowledge which was not there before, but to turn the mind's eye towards light so that it might see for itself." ...Plato's advice to educators(429-347BC)

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 Author Topic: Centre of Gravity problem  (Read 27290 times) 0 Members and 1 Guest are viewing this topic. Click to toggle author information(expand message area).
Khaldoun-Habboub
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 « Embed this message on: February 20, 2006, 06:02:14 pm » posted from:Damascus,Dimashq,Syrian Arab Republic

Hey,
If a uniform metre rule has a 4N weight hanging from one end, and the rule balances when suspended from a point 0.1m from that end. What would be the weight of the rule??? cheers
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Fu-Kwun Hwang
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 « Embed this message Reply #1 on: February 21, 2006, 10:27:28 am »

May be I did not fully understand your question.
But why the weight of the rule will be changed when suspended from different points?
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Khaldoun-Habboub
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 « Embed this message Reply #2 on: February 22, 2006, 04:17:45 pm »

You are absolutely right, but the question was stated exactly the same way I stated above.
It came from a physics text book by Oxford. :!:
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hy2220N11411E
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 « Embed this message Reply #3 on: March 23, 2006, 12:45:26 am »

The orginal question should be interpreted this way:
a uniform metre rule (or ruler) means a beam of 1 metre in length;
a 4N weight (a separated heavy object) being hanged from one end, exerting a downward force;
the rule is being hanged 0.1m from the end with the 4N weight, exerting an upward force (the tension);
uniform metre rule means the CG (centre of gravity) is 0.5m from either end, and the weight of the rule is producing another downward force;

Let W = weight of the rule, T = the tension to "hang" the rule

taking moment about the end with the "4N weight", then
(0.1)(T) = (0.5)(W)

all upward forces = all downward forces, then
T = W + 4

by solving the simultaneous equations
W = 1

so the weight of the rule is 1 N

Hope my words help.
Cheers.
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bluebearqq
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 « Embed this message Reply #4 on: February 20, 2011, 05:56:51 am » posted from:Hamilton,Waikato,New Zealand

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"That their main business was not put into the mind knowledge which was not there before, but to turn the mind's eye towards light so that it might see for itself." ...Plato's advice to educators(429-347BC)