THEgurlxo
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Hi, can someone help with this question because I've been stuck on it for so long. I don't understand why when resolving vertically it is P sin alpha rather than P cos alpha. And solution bank shows the answer as 7.2N, but the answers at the back of the book are saying 11.4N. Someone help please.
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RDKGames
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(Original post by THEgurlxo)
Hi, can someone help with this question because I've been stuck on it for so long. I don't understand why when resolving vertically it is P sin alpha rather than P cos alpha. And solution bank shows the answer as 7.2N, but the answers at the back of the book are saying 11.4N. Someone help please.
If you can convince yourself that the little decomposition on force P which I have drawn is true, then it's obvious why the perpendicular component is including sin(alpha) rather than cos(alpha).

Also P = 7.2N is the correct answer.

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THEgurlxo
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(Original post by RDKGames)
If you can convince yourself that the little decomposition on force P which I have drawn is true, then it's obvious why the perpendicular component is including sin(alpha) rather than cos(alpha).

Also P = 7.2N is the correct answer.

Thank you, and can you show the trig behind that??/ Because im still a little confused because I thought the vertical component would be cos alpha as it the sane as the other triangle drawn ( for the 2gN)
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RDKGames
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(Original post by THEgurlxo)
Thank you, and can you show the trig behind that??/ Because im still a little confused because I thought the vertical component would be cos alpha as it the sane as the other triangle drawn ( for the 2gN)
You mean 'perpendicular component' rather than 'vertical component' ??

anyway I am not sure what trig there is to show. If you are happy with the angle being where it is (ie convince yourself it must be there) then clearly the perpendicular component of P must be Psin(alpha). The perpendicular side of that triangle is the opposite side to the angle, so it must be sine for it.
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Anonymouspsych
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(Original post by THEgurlxo)
Thank you, and can you show the trig behind that??/ Because im still a little confused because I thought the vertical component would be cos alpha as it the sane as the other triangle drawn ( for the 2gN)
Since alternate angles are equal, it means that the angle @RDKGames has drawn must also be alpha. From the triangle it should be obvious that the perpendicular (not vertical!) component is Psin(alpha) and the parallel component to the slope is Pcos(alpha)
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