# Mechanics equilibrium of rigid bodies

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I'm stuck on part a) of the question. I think you are supposed to take moments about A. I not sure how to do this as you don't get given an angle therefore I don't know what the value of cos theta will be. Thanks

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#2

(Original post by

I'm stuck on part a) of the question. I think you are supposed to take moments about A. I not sure how to do this as you don't get given an angle therefore I don't know what the value of cos theta will be. Thanks

**Anonymous_4657**)I'm stuck on part a) of the question. I think you are supposed to take moments about A. I not sure how to do this as you don't get given an angle therefore I don't know what the value of cos theta will be. Thanks

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(Original post by

Well you've got a right-angled triangle and two of the sides: That's enough to work out any angles you need.

**ghostwalker**)Well you've got a right-angled triangle and two of the sides: That's enough to work out any angles you need.

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#4

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I'm still a bit confused on what to do. Please may you help. In the answers it says cos theta is 2/ square root 13.

**Anonymous_4657**)I'm still a bit confused on what to do. Please may you help. In the answers it says cos theta is 2/ square root 13.

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#5

**Anonymous_4657**)

I'm still a bit confused on what to do. Please may you help. In the answers it says cos theta is 2/ square root 13.

So, what's the line of action of the force, and what's its perpendicular distance?

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I just don't understand how they got the value of Cos theta. ghostwalker

Last edited by Anonymous_4657; 1 month ago

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#7

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I just don't understand how they got the value of Cos theta. ghostwalker

**Anonymous_4657**)I just don't understand how they got the value of Cos theta. ghostwalker

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(Original post by

See my post #5 to start. I don't know where you're upto, what you've been able to understand so far. What angle theta is. You've not posted the markscheme you're looking at, and I'm not a ...... mind reader.

**ghostwalker**)See my post #5 to start. I don't know where you're upto, what you've been able to understand so far. What angle theta is. You've not posted the markscheme you're looking at, and I'm not a ...... mind reader.

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**ghostwalker**)

See my post #5 to start. I don't know where you're upto, what you've been able to understand so far. What angle theta is. You've not posted the markscheme you're looking at, and I'm not a ...... mind reader.

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#10

They get the value of cos theta by just using trigonometry as you know the ratio of two if the sides so you can find the third by using pythagoras then from there you can find the exact value of cos theta

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#11

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Can you help me understand how they get the value of cos theta?

**Anonymous_4657**)Can you help me understand how they get the value of cos theta?

Cos theta = adjacent / hypotenuse.

Adjecant is 2a

Hypotenuse, via pythagoras, is

Hence

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(Original post by

So, theta is in the top left.

Cos theta = adjacent / hypotenuse.

Adjecant is 2a

Hypotenuse, via pythagoras, is

Hence

**ghostwalker**)So, theta is in the top left.

Cos theta = adjacent / hypotenuse.

Adjecant is 2a

Hypotenuse, via pythagoras, is

Hence

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#13

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Thanks. I was getting a bit confused where theta was. I didn’t realise it was in the top left. It never specified in the question.

**Anonymous_4657**)Thanks. I was getting a bit confused where theta was. I didn’t realise it was in the top left. It never specified in the question.

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(Original post by

Theta is top left in the markscheme (diagram at top), but if you were doing the question without having seen the markscheme you could have chosen a different angle to be theta - e.g. the bottom right. Either would be fine, just give slightly different working, but getting the same results.

**ghostwalker**)Theta is top left in the markscheme (diagram at top), but if you were doing the question without having seen the markscheme you could have chosen a different angle to be theta - e.g. the bottom right. Either would be fine, just give slightly different working, but getting the same results.

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