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# OCR M1 Forces and Equilibrium watch

1. Hi guys, I've got this question for homework and I have honestly been on it now for an hour easy...I just have no idea how to do it. I ended up finding the markscheme and I don't even understand why they have that answer....would someone please be able to give me a hand?

Two small rings A and B are attached to opposite ends of a light inextensible string. The rings are
threaded on a rough wire which is fixed vertically. A is above B. A horizontal force is applied to a
point P of the string. Both parts AP and BP of the string are taut. The system is in equilibrium with
angle BAP = α and angle ABP = β (see diagram). The weight of A is 2 N and the tensions in the parts
AP and BP of the string are 7 N and T N respectively. It is given that cos α = 0.28 and sin α = 0.96,
and that A is in limiting equilibrium.
(i) Find the coefficient of friction between the wire and the ring A. [7]
(ii) By considering the forces acting at P, show that T cos β = 1.96. [2]
(iii) Given that there is no frictional force acting on B, find the mass of B.

Preferably some help on all of the parts but no worries if that's asking too much!

Much appreciated,
Matt
2. Sorry you've not had any responses about this. Are you sure you've posted in the right place? Here's a link to our subject forum which should help get you more responses if you post there.

Just quoting in Danny Dorito so she can move the thread if needed
Spoiler:
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(Original post by Danny Dorito)
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3. Hey Buddy, I've just done the question so it is doable. The most important thing with a question like this is to draw a good diagram. Then just equate forces.

For (i), come up with equations for the vertical and horizontal equilibrium at A.

for (ii), do similar things at P

And do the same at B for (iii)
4. Sorry for the late reply...as you know, A levels can get quite busy Yeah I realised that I had been drawing the tension acting in the wrong direction which messed up my answer. Cheers mate!

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