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# M1 - Force on pulley Watch

1. I've seen this question come up a few times on past papers and on Arsey's model answers he uses the formula 2TCos((90 - alpha)/2) where alpha is the angle between the horizontal and the inclined plane.

The formula works but I don't really understand where its come from? Can someone please explain this for me? (I don't like using formulas that I don't understand). I have attached the 2015 question as an example. (Tension is 6.53N, acceleration is 3.27 ms-2).

Also, is there a way to work out the force from 'first principles' (for want of a better word) just in case they ask a question where the formula can't directly be used? ; ie work it out using a vector triangle, cosine rule etc?

2. Hi. This video should help you with calculating the force acting on the pulley-:
3. (Original post by TheRandomGenius)
I've seen this question come up a few times on past papers and on Arsey's model answers he uses the formula 2TCos((90 - alpha)/2) where alpha is the angle between the horizontal and the inclined plane.

The formula works but I don't really understand where its come from? Can someone please explain this for me? (I don't like using formulas that I don't understand). I have attached the 2015 question as an example. (Tension is 6.53N, acceleration is 3.27 ms-2).

Also, is there a way to work out the force from 'first principles' (for want of a better word) just in case they ask a question where the formula can't directly be used? ; ie work it out using a vector triangle, cosine rule etc?

Watch this.
4. (Original post by Zacken)
Watch this.
Thanks - got it now.
5. (Original post by TheRandomGenius)
Thanks - got it now.
No worries.

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