Indian Friends Group III

Haha, I know that feeling. Come visit us in the Maths forum with questions you have! General tips off the top of my head

Circular motion:

1) Horizontal: Resolve vertically - the acceleration will always be 0 so F = ma = 0. Resolve horizontally: acceleration is rw^2 or v^2/r.

2) Vertical:

RESOLVE GOING TOWARDS THE CENTRE OF THE CIRCLE. CENTRE OF THE CIRCLE. CEEEEEEEEENNNNNNTTTTTTTRRRRRREEEEEEEEEE OFFFFFFFFFF TTTTTTTTHEEEEEEEEEEEEEE CCCCCCCCCCIIIIIIIIRRRRRRCCCCCCCCCLEEEEEEEE. Otherwise, all the maths will fall apart. Going towards the centre of the circle, a = rw^2 or v^2/r.

Literally every question will require you to use energies. Just remember that energy at the start = energy at the end. In general, this'll just be

Energy at start = 0.5mu^2 (KE at start)
Energy at end = 0.5mv^2 + mgh (final KE + PE gained)

To work out h, use Pythagoras. It's usually like r - rcos(theta).

So 0.5mu^2 = 0.5mv^2 + mgh (nrg at start = nrg at end) (don't you just love that abbreviation? nrg = energy)

Kinematics:

Almost every question just requires F = ma = mvdv/dx

Strings/springs:

To prove S.H.M., use F = ma and remember to let x = the displacement and x double dot be the acceleration AND MAKE IT GO IN THE DIRECTION OF INCREASE x OR YOU WON'T GET THE NEGATIVE SIGN IN S.H.M.

The rest of the questions are again just energy questions, remembering that you have GPE + KE + EPE + Work Done.

Centres of mass:

Just write down every shape's volume/area. The total shape will then just have all of the other shape's area + volume. Then below it write down where the individual parts of the shape have their centres of mass. Multiply them together and you'll get like

5A + 2A = 3Ay (y bar)

Can't think of much else to say .

I did the stupidest thing in my M3. I did the paper and had about 20 mins left. Checked it once through and then just sat there for like 5 or 6 mins. With 10 mins to go, I thought I'd check the back, just for a laugh. Oh ****, another question on the back. Think it was either SHM or circular motion (June 2004 if you want to see). I did it in the end, but it was kinda rushed.

Yep SHM
Sorry, I just think that it is funny when people don't check the last page of the exam, I keep flipping pages until it says End of Questions at the bottom of the page.

Did you manage to get a grade you were happy with in M3? If so, who cares

Besides the work done equation you have written there, that is just absolutely brill
I don't get that equation

At the risk of turning this society into another Maths society, what don't you understand? I always found it confusing when doing M2 and ended up with a C but someone explained it well to me this year:

If something moves 5m and there's friction acting against it, you get work done. The work done (which is apparently an energy) is force * distance = friction * displacement. So if something moves 5m against a frictional force of 20 N, the work done (WD) is 20 * 5 = 100 J.

Now then, if you start moving at 5 m/s and up moving at 3 m/s (with a mass of 1 kg for convenience) and you've moved 7m in this process, then:

KE at start = 0.5 * 1 * 5^2 = 12.5 J

KE at end = 0.5 * 1 * 3^2 = 4.5 J

But hang on, energy at start = energy at end. Where the hell does 8 J of energy go? The answer is "work done". Why? Newton's first law tells us that you'll keep moving at the same speed, in the same direction, unless if a force acts on you (I think). In this case, our force must have been friction. To calculate the work done against friction, we just do distance * frictional force = 7Fr (I'm using Fr to mean frictional force = mu * R in limiting equilibrium, whatever that means).

So then

Energy at start: KE at start

Energy at end: KE at end + Work done vs Fr.

Energy at start = energy at end

It's like the KE at the start gets CONVERTED into work done.

KE at start = KE at end + Work done vs Fr
12.5 = 4.5 + Work done vs Fr

We can see that the work done is 8 J. And we could find the frictional force because we know work done vs Fr = 7 Fr, so 8 = 7Fr and hence Fr = 8/7.

M3 questions will like to throw in GPE as well + EPE as well. But just think of it as what you have at the start and what you have at the end.

Hey,Kemchor,Namaste,Sat Sri Akal

British Hindu Here

Indian heritage! (Gujarati)

Amit Patel

Mechanics ;yes;

I messed up M2 big time Sway...but hopefully I can swap M1 for M3 and therefore I don't need to do well in it!

I don't see why not...
There's nothing to say that I can't have any applied module in normal maths...
I just can't have more than M1 or S1 or D1 in my FMaths!