username3810906
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Anyone help With B and C

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BTAnonymous
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I'd reword a) to 'For a system in equilibrium, sum of clockwise moments = sum of anticlockwise moments'.

b) find perpendicular distance from A to the wire. Should be 0.3 x Sin(30). Then calculate the moments of the weight of the plank and the vase then solve for tension.

c) You know the force/tension the wire experiences and you know the cross-sectional area so you can calculate the stress then rearrange for strain.

 Youngs modulus = \frac{stress}{strain}
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Eimmanuel
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(Original post by BTAnonymous)
I'd reword a) to 'For a system in equilibrium, clockwise moments = anticlockwise moments'.
...
If this is what is written in A level physics exam, I doubt the candidates would get the full 2 marks, you will be lucky to get 1 mark.
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BTAnonymous
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(Original post by Eimmanuel)
If this is what is written in A level physics exam, I doubt the candidates would get the full 2 marks, you will be lucky to get 1 mark.
That's the textbook definition and definition I've seen in past papers.

edit: should be "sum of..." clockwise/anticlockwise.
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Eimmanuel
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(Original post by BTAnonymous)
That's the textbook definition and definition I've seen in past papers.

edit: should be "sum of..." clockwise/anticlockwise.
I doubt that the textbook definition is just like that.

Principle of Moments states that when an object is in equilibrium, the sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about the same point.
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BTAnonymous
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(Original post by Eimmanuel)
I doubt that the textbook definition is just like that.

Principle of Moments states that when an object is in equilibrium, the sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about the same point.
Yeah I see what you mean. Past papers however haven't awarded marks for 'about any point' phrase.
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Eimmanuel
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(Original post by BTAnonymous)
Yeah I see what you mean. Past papers however haven't awarded marks for 'about any point' phrase.
I am not sure which examination board does that.
CIE expects both "sum" and "about a point" (or about any point).
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BTAnonymous
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(Original post by Eimmanuel)
I am not sure which examination board does that.
CIE expects both "sum" and "about a point" (or about any point).
I do AQA. In their textbook they do have about a point but it's not a necessary mark point. It does make sense though now that you mention it, as it is an important part of the principal.
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