Mega A Level Maths Thread MK II

Haven't you heard how rowdy mathematicians can get?

Seems like lots of ppl posting on this thread have lots of warning points... Wonder why..

Yh 8c I believe it was, I thought something similar; that the vertical velocity would be the same but in the opposite direction but I got it all wrong. Still managed a method mark for using v = u + at

That's fair enough then and that would've been the only place I dropped marks too, however I put the correct answer for the impulse question but then decided to cross it out as I actually thought it wouldn't make much sense of the direction afterwards if it got hit at that angle, so I lost a good amount of marks there but still got 65/75 in the end which wasn't all that bad considering the grade boundaries

LOOL good luck I told you i'd find a good question
Felix here:
There is a rabbit that runs in a perfect circle of radius r with a constant speed v. A fox chases the rabbit, starting from the center of the circle and also moves with a constant speed v such that it is always between the center of the circle and the rabbit. How long will it take for the fox to catch the rabbit?

Gotta love the method marks you get for certain things eh?

Seriously though, this thread has some rebellious mathematicians

67/75 for 100 UMS! I wouldn't mind something like that for the real thing , the impulse question seemed scary at first but once you resolved it it was fine and seeing the modulus in COM was like ... but it made sense at the end since you can't have negative distance, apart from those 3 questions it was a standard paper .

Nah , it would be annoying if you lost method marks yet ended with the correct answer

I went through one of those papers... they are pretty weird, I had no idea MEI made such papers.

I'm not sure if you can actually revise for it, seems more like a test of mathematical thinking/logic if you get me. Maybe do some past papers for familiarisation but other than that I'm not too sure what you can do.

I can't seem to form a suitable equation for the components of v.

Defo on the right track!
The first two lines are perfect try forming a full a differential equation?
If $\theta=\frac{Vt}{r}$ what is $\theta'?$

That's not a problem.
$\theta' = \dfrac{d\theta}{dt} = \dfrac{v}{r}$
The issue is I can't get hold of an expression for either:
$\dfrac{dr}{dt} \ \mathrm{Or} \ \dfrac{dr}{d\theta}$
This'd allow me to form and solve a differential equation (hopefully seperable ) of the form:
$t = \displaystyle\int^R_0 f(r) \ dr$

Ahh I see, does this help ?
For this problem it is advisable to introduce polar coordinates (r and ϕ). The rabbit runs at speed v on a perfect circle with radius R. Therefore, ϕ=vt/R (you know all of this)
As the fox stays between the center and the rabbit, it is at the same ϕ. The fox's speed (which is constant) has two component (prime denotes the derivative with respect to time)
this means...

$v=\sqrt{something^2+something^2 \theta'^2}$

That marks for 100 UMS would be just lovely in the real thing And yeah that's what I did at first but then I started to act it out with my arms and it literally didn't seem possible so I went down the other route which just happened to be incorrect I also got horrified by the modulus sign in COM and just thought I'll be getting about 40/75 for this paper but like you said it all made sense at the end, however I missed out a factor in the process so had to pick through my method to find the mistake to correct it which took a good 10 minutes!

Yeah it wasn't as bad after doing them all, however I wouldn't have liked that in the actual exam, neither would I like June 2012 with the COM question in that one too!

I feel those 2 were the hardest really.

I can't seem to form a suitable equation for the components of v.

Lol true, that happens with me in C2, so this time I showed every lil' step lool
Its good when you don't know what to do or make a silly mistake

Did M2 Jan 2010 for the first time and got 70 , I wouldn't say it's that bad although my method for quite a few was different to the MS. Dropped all the marks on the last question as I didn't know what to do. I mean why did they use dy/dx for projectiles?

You started M3 already?

I haven't tried June 2012 yet so I can't comment, yet I've had a quick look and that impulse and COM question do look kind of spooky! I've still got quite a few papers to do

I know that:
$v=\sqrt{(SOMETHING)^2 + r^2\left(\dfrac{d\theta}{dt} \right)^2}$
I said so in the last post, the other something is what I cannot derive

You started M3 already?

I went at a snails pace throughout the C2 exam, there was no way I was gonna make a silly mistake this time

Oh yeah, my bad x_x I need to learn how to read.
Right you have information about 3 things, this 'something squared' is one of these intitials...tbh this is the only difficult part, after you can derive this the questions average

I haven't seen the question but I'm going to assume they used it to find the maximum height of the path of trajectory (or something along those lines).

Nah, the question asked to find the vertical component of the velocity when it's travelling at right angles to it's initial velocity.



Full question is here, part c)