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"In theory, theory and practice are the same. In practice, they are not." ..."Albert Einstein (1879~1955, Mathematical physicist, Nobel Prize 1921-Physics)"

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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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"In theory, theory and practice are the same. In practice, they are not." ..."Albert Einstein (1879~1955, Mathematical physicist, Nobel Prize 1921-Physics)"