Edexcel Mathematics: Mechanics M3 6679 01 - 17 May 2017 [Exam Discussion]

Hi, could someone please tell me what M3 requires in terms of knowledge about volumes, surface areas etc of shapes. Thank you.

Reply 124

TSRUser12345

4

Original post by Major-fury

Hi, could someone please tell me what M3 requires in terms of knowledge about volumes, surface areas etc of shapes. Thank you.

Same as C4

Reply 125

Original post by TSRUser12345

Same as C4

what are the ones needed for c4 lol. I've already taken c4 a while ago :/

Reply 126

physicalgraffiti

Hi guys,

I'm a bit confused on a couple calculus examples in Chapter 5 (Statics) in the Edexcel M3 textbook.

First off, do we have to use the formula for Mx̅ and M then divide Mx̅ by M to get x̅ (and the same thing for ȳ?)
It just doesn't make sense to do that when the x̅ and ȳ formulae are given to us. Like in one example they'll do it the way I described above and in another example they'll just use the x̅ and ȳ formulae to get the answers straight away. Is there a reason to do it the first method or is it okay to do it just using the x̅ and ȳ formulae without needing to calculate the mass and stuff?

Many thanks

Reply 127

Could someone help me with Question 2 jan 2007 please. I can get to the bit where we find the centre of mass of the cone etc. but i can't seem to visualise where the triangle comes from with the upward vertical.

Reply 128

tiny hobbit

Original post by Major-fury

Could someone help me with Question 2 jan 2007 please. I can get to the bit where we find the centre of mass of the cone etc. but i can't seem to visualise where the triangle comes from with the upward vertical.

The triangle goes from A to G to the centre of the circular base, with the right angle at the centre of the base.

Reply 129

Original post by tiny hobbit

The triangle goes from A to G to the centre of the circular base, with the right angle at the centre of the base.

Sorry but I don't quite follow. Aren't we trying to calculate the angle made with the upward vertical? If possible could you draw a diagram, I think i'm overlooking something.

Reply 130

tiny hobbit

Original post by Major-fury

Sorry but I don't quite follow. Aren't we trying to calculate the angle made with the upward vertical? If possible could you draw a diagram, I think i'm overlooking something.

Yes. This is the same size as the angle at G in the triangle I was talking about.

Diagram from mark scheme attached.

Cone question.doc30.7KB

Reply 131

Original post by tiny hobbit

Yes. This is the same size as the angle at G in the triangle I was talking about.

Diagram from mark scheme attached.

Could you explain why theta is equal to that angle please?

Reply 132

tiny hobbit

Original post by Major-fury

Could you explain why theta is equal to that angle please?

G (the centre of mass) will be vertically below A, the point of suspension.

So this angle is, like the one marked theta, between a vertical line and the axis of the cone.

Reply 133

Original post by tiny hobbit

G (the centre of mass) will be vertically below A, the point of suspension.

So this angle is, like the one marked theta, between a vertical line and the axis of the cone.

Thanks. I think I understand it. At least a little better :tongue:

Reply 134

kavindajd

Original post by physicalgraffiti

Hi guys,
It just doesn't make sense to do that when the x̅ and ȳ formulae are given to us.

I don't think those formulae are given - you have to memorise them.

Reply 135

Jamvicious

Original post by physicalgraffiti

Hi guys,

I'm a bit confused on a couple calculus examples in Chapter 5 (Statics) in the Edexcel M3 textbook.

First off, do we have to use the formula for Mx̅ and M then divide Mx̅ by M to get x̅ (and the same thing for ȳ?)
It just doesn't make sense to do that when the x̅ and ȳ formulae are given to us. Like in one example they'll do it the way I described above and in another example they'll just use the x̅ and ȳ formulae to get the answers straight away. Is there a reason to do it the first method or is it okay to do it just using the x̅ and ȳ formulae without needing to calculate the mass and stuff?

Many thanks

If you can do it using the formulae then you probably should, unless the question specifies not to, but its not always possible to do it using the formulae, so you'd have to use the first method

Original post by kavindajd

I don't think those formulae are given - you have to memorise them.

Pretty sure we're given formulae for centres of mass of hemispheres and cones

Reply 136

kavindajd