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    Q14 - image attached.
    Also Q15. However if I can understand Q14, the whole concept should click. There's no mention of how to do it in the book. Cheers!

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    (Original post by stuart_aitken)
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    What is it about the question that's causing you a problem?
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    (Original post by ghostwalker)
    What is it about the question that's causing you a problem?
    I'm not sure how to find the centre of mass of a semi-circle. Looks like it requires integration? It's mentioned in the next chapter of the book, but that chapter isn't part of the syllabus, so I presume there's another way to do it?

    Logically I would say you can draw another circle opposite the first one, and from there you'd see that the mass of the leftover bits can be discounted as they essentially cancel from the equation.

    Aaaaaah done it! Yep it can be done geometrically.

    Solution image attached for all who might be interested.

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