# M3 Centre of Mass QuestionWatch

Announcements
#1
Hey, I've just done the OCR MEI June 2012 paper and I couldn't work out how to do the last part of question 4

I've looked at the mark scheme and I have no idea why the situation ends up as it is - why the reaction to the surface passes through O.

The COM is from O, ie from the center of the surface.

Question 4bii) from http://www.mei.org.uk/files/papers/m3_june_2012.pdf
Mark scheme is at the bottom of the document.

Thanks!
0
3 years ago
#2
(Original post by Duskstar)
Hey, I've just done the OCR MEI June 2012 paper and I couldn't work out how to do the last part of question 4

I've looked at the mark scheme and I have no idea why the situation ends up as it is - why the reaction to the surface passes through O.

The COM is from O, ie from the center of the surface.

Question 4bii) from http://www.mei.org.uk/files/papers/m3_june_2012.pdf
Mark scheme is at the bottom of the document.

Thanks!
Alhough I do edexcel I will be home in 15 minutes. I will do this question. Main thing to note is that the slope is tangent to the circle and all tangents are perpendicular to the radius. That sorts the question out easily. Note that G lies on this line aswell.
Reaction is perpendicular to friction(the slope) hence why it passes through O. Not that Fr and R act at piint of contact and G acts at the COM. Take moments about O.

Posted from TSR Mobile
3
#3
(Original post by physicsmaths)
Alhough I do edexcel I will be home in 15 minutes. I will do this question. Main thing to note is that the slope is tangent to the circle and all tangents are perpendicular to the radius. That sorts the question out easily. Note that G lies on this line aswell.

Posted from TSR Mobile
Thanks, long time no speak too :P

And actually that sorts it out - the circle has to sit tangent to the slope so the reaction will go through the centre, and I can do the question from there

Idk why I missed over that but I just couldn't get an image of how it would sit on a slope haha
0
3 years ago
#4
(Original post by Duskstar)
Thanks, long time no speak too :P

And actually that sorts it out - the circle has to sit tangent to the slope so the reaction will go through the centre, and I can do the question from there

Idk why I missed over that but I just couldn't get an image of how it would sit on a slope haha
Yep
I did a very similar question on a Delphis paper.

Posted from TSR Mobile
0
X

new posts

### 1,478

people online now

### 225,530

students helped last year
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### University open days

• Sheffield Hallam University
Tue, 20 Aug '19
• Bournemouth University
Wed, 21 Aug '19
• University of Dundee
Mon, 26 Aug '19

### Poll

Join the discussion

#### Are you going to self-release into Clearing?

Yes I've pressed the button (76)
17.31%
No I'm happy with my uni offer (281)
64.01%
Not yet but I am planning to (21)
4.78%
Not yet but I might (61)
13.9%