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Is there a reason why I can't resolve for the forces like this?

http://filestore.aqa.org.uk/subjects/AQA-PHYA2-QP-JUN14.PDF

Q(3)(a)(iv)

I understand I need to resolve the component of T that is perpendicular to the lever/rod/whatever the hell the thing is.

So initially I resolved like this (Which is correct according to the mark scheme)



But then I thought, surely if I just drew my triangle differently I could resolve like this too?


If anyone could explain why resolving it like the second picture won't work. that would be great. It's just that I don't want to be resolving incorrectly in the exam so I have thought of different ways to try and find the force.

Thanks!
Reply 1
Avatar for pri12321
pri12321
3
Hi, as you said the first resolution is correct. The second one isn't correct because now T is no longer the hypotenuse. If you think about it, this means that you are saying the vertical component of T is bigger than T itself, which doesn't make sense. When resolving you need to make the force the hypotenuse Good luck with the exam :smile:
Original post by TheBride
Hi, as you said the first resolution is correct. The second one isn't correct because now T is no longer the hypotenuse. If you think about it, this means that you are saying the vertical component of T is bigger than T itself, which doesn't make sense. When resolving you need to make the force the hypotenuse Good luck with the exam :smile:


Ah I see now!

So does this mean that the force that the exam board labelled "T" is the RESULTANT force and the force I labelled in the first picture A, is the vertical component?
Thanks for the reply +rep
Reply 3
Avatar for pri12321
pri12321
3
Original post by CrazyFool229
Ah I see now!

So does this mean that the force that the exam board labelled "T" is the RESULTANT force and the force I labelled in the first picture A, is the vertical component?
Thanks for the reply +rep


Yes A is the vertical component of T, T is the actual force causing the horizontal and vertical components, but be careful of saying "resultant" because that's used more for adding/subtracting different forces . Also thanks for the rep! :smile: Also just quickly although I said "vertical" in this case it's actually at a slight angle- but you get the gist!
(edited 7 years ago)
Original post by TheBride
Yes A is the vertical component of T, T is the actual force causing the horizontal and vertical components, but be careful of saying "resultant" because that's used more for adding/subtracting different forces . Also thanks for the rep! :smile:


Thanks again!

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