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M2 Lamina and Hanging Problem

Hello, I have a quick question about hanging problems involving Laminas.
Generally I can do the question were I have find the angle between and edge and a vertical.
The only problem is, I find it hard to identify the correct angle they are asking for.
For example on Question 4 on this paper
http://store.aqa.org.uk/qual/gceasa/qp-ms/AQA-MM2B-W-QP-JAN07.PDF

My teacher wasn't very helpful in explaining why it was the 63 degree angle and not the 27 degree one. I drew my triangle such that tan(x)=0.5

thanks

Reply 1

dragonkeeper999

"find the angle between the edge AB and the vertical" - doesn't this explain it!? You have to make sure you've drawn the diagram right I guess...
EDIT: oh, I see why you're confused, the line AB goes through the pivot point. Ummm... just make it clear in your answer which angle you have calculated, for example by drawing a diagram. It wouldn't hurt to calculate the other angle too, just in case.

(edited 11 years ago)

Reply 2

TenOfThem

I struggle to see the problem too as it seems clear in the question

Can you post your diagram

Reply 3

jarasta

Original post by TenOfThem

I struggle to see the problem too as it seems clear in the question

Can you post your diagram

Okay, give me a sec.

Reply 4

jarasta

Original post by TenOfThem

I struggle to see the problem too as it seems clear in the question

Can you post your diagram

here you go, so the question is why the angle labelled phi and not the one theta. As far as I can see they are both vertical. At this point im not even sure i know what the phrase means :mad:

thanks

m2 question.jpg504.7KB

Reply 5

jarasta

Original post by dragonkeeper999

if I have both angles and write I dont know what exactly the question is asking for in terms of the angle (which vertical exactly xD). Would they mark both answers?

Reply 6

TenOfThem

Original post by jarasta

here you go, so the question is why the angle labelled phi and not the one theta. As far as I can see they are both vertical. At this point im not even sure i know what the phrase means :mad:

thanks

Ah

A complete lack of understanding

The point of the CoM is that it will be directly below the point of suspension

So the line from x through the CoM is vertical

Reply 7

TenOfThem

Original post by jarasta

if I have both angles and write I dont know what exactly the question is asking for in terms of the angle (which vertical exactly xD). Would they mark both answers?

Reply 8

jarasta

Original post by TenOfThem

Ah

A complete lack of understanding

The point of the CoM is that it will be directly below the point of suspension

So the line from x through the CoM is vertical

Aaaahhh thats what the vertical is! This is news to me, good news. Yeah that makes perfect sense now :biggrin:

, Thank you, :').
Another question, whilst you are here.
When it asks, the angle between AB and the horizontal, which side do you take to be the horizontal. In either question 4 on this paper (http://store.aqa.org.uk/qual/gce/pdf/AQA-MM2B-W-QP-JAN11.PDF) or the question i've already posted