# Oxford Physics Students and ApplicantsWatch

9 years ago
#361
(Original post by blueJ-)
although i guess the knowledge that radius^3 is proportional to time period^2 wouldn't harm
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9 years ago
#362
The body's excretion is exponential too- look up 'biological half life'. If you think about it, this makes sense since the rate at which a chemical is processed by the body would usually depend on the concentration.
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9 years ago
#363
jeez, had a look at some of the physics olympiad paper 2's, they're extremeley hard...
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9 years ago
#364
Thanks for this helpful thread! How would you go about doing question 10, with the geometric and arithmetic progressions?
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9 years ago
#365
Oh my goddd more people applying to Oxford for physics... ahh the competition

Hi...

(I'm trying to do the rest now)
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9 years ago
#366
ok, uh, PAT 2008.
a few troubles,
question, 3, I don't really know what to do.
question 7, do you just differentiate and then put in x as 1/4 and work it out to a good enough degree of accuracy (1.3?) or is there a better way of doing it?
And question 9, if numbers 5 and 6 are obtained three times as often as 2,3 and 4, then surely if 2,3 and 4 are each obtained 1/6 of the time, then 5 and 6 would be 3/6 of the time, but that would add up to 9/6 which isn't possible. And can it be over a number greater than 6 if it's a six sided dice? I swear not...

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9 years ago
#367
(Original post by blueJ-)
don't think about using laws, just think through it logically for example, the question with two batteries & 3 bulbs, with one bulb on a wire through the middle

for a moment imagine the wire isn't there,; what's the voltage between the two batteries if, say, each battery is 1V? next, what would then be the voltage between the two bulbs if each battery had a voltage of 1V. Now compare the voltage at each point, if you were to put a voltmeter between the points, what would it say is the POTENTIAL DIFFERENCE between the two points?
Hey BlueJ

You seem to know your stuff so I thought I'd ask you some questions:

The bulb question you were trying to answer above

Phy Oct 07: 14 (Pendulum)

Phy May 06: 14 Why is the speed of the weight half of the lift? and e)ii)

Phy Nov 08: 23, 27c and onwards

Thank you so much if you can find the time to help me
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9 years ago
#368
(Original post by Mighty Grandiose Noble Knight)
Hey BlueJ

You seem to know your stuff so I thought I'd ask you some questions:

The bulb question you were trying to answer above

Maths Oct 07: 12

Phy Oct 07: 14 (Pendulum)

Phy May 06: 14 Why is the speed of the weight half of the lift? and e)ii)

Math Nov 08: 7

Phy Nov 08: 23, 27c and onwards

Thank you so much if you can find the time to help me
for nov 08 number 7 differentiate to get 1 + 0 +0 +0 .... so a is 1

then fr when x=1/4 it is 1 + 1/4 + 1/4^2 +1/4^3 ... summation of geometric series therefore a/1-r therefore 1/(1-1/4) which is 4/3
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9 years ago
#369
(Original post by Lamo)
ok, uh, PAT 2008.
a few troubles,
question, 3, I don't really know what to do.
question 7, do you just differentiate and then put in x as 1/4 and work it out to a good enough degree of accuracy (1.3?) or is there a better way of doing it?
And question 9, if numbers 5 and 6 are obtained three times as often as 2,3 and 4, then surely if 2,3 and 4 are each obtained 1/6 of the time, then 5 and 6 would be 3/6 of the time, but that would add up to 9/6 which isn't possible. And can it be over a number greater than 6 if it's a six sided dice? I swear not...

In 3, (1+x)m+1=(1+x)(1+x)m and (1-2x)m=(1+[-2x])m. It's then just a matter of expanding the expressions.
When you differentiate the expression in 7, the coefficients of the xn terms cancel with the denominators of the fractions, so you have a geometric series (you should know how to work out the sum to infinity).
For 9, recognise that the sum of the probabilities of all the numbers must add up to 1; it's then easy to work out the probability of each number.
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9 years ago
#370
(Original post by 05wilsea)
for nov 08 number 7 differentiate to get 1 + 0 +0 +0 .... so a is 1

then fr when x=1/4 it is 1 + 1/4 + 1/4^2 +1/4^3 ... summation of geometric series therefore a/1-r therefore 1/(1-1/4) which is 4/3
Thank you so much. Just realized that x=0 was given. Damn.
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9 years ago
#371
hmmm that's a bunch of questions there... you should try to put down some working, i find alot when i try to articulate the exact problems i'm having the answer comes out but anyways i'll get you started;

question 12/maths/2007

realise here that the perimeter can be anything, you can scale up and down triangles keeping side length ratio's intact so for easiness take p to be 1. now you know that the sides are 1 - 2x, x & x. now come up with a function for the area of the triangle in terms of x, you'll have to play around a bit with Pythagoras here. next, how do you usually find out when a function is greatest for a value of x? (maximum?)

27c/physics/2008

you know how fast it's travelling when it 'hits' the ground, call that u, you know it's stopping distance, 1mm, call that s, you know it's speed when it's come to a halt, 0, call that v, ring a bell? =P

then enlist the help of Newtons second equation.

i'll try to (or someone else will) get some help down for the other questions you asked about tomorrow
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9 years ago
#372
Uh, do we get some spare paper to make notes and quick calculations and such on it? The PAT site mentions "pen and paper" but there is no additional space on the sample paper so I'm confuzzled.
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9 years ago
#373
Does anyone know what kind of information is required by "Phases of the moon and eclipses" on the PAT syllabus?
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9 years ago
#374
(Original post by Mr Nonsense)
I got 400kPa for the pressure cooker one I think - whatever was listed in the original poster's answers.

After 1 hour, the amount of radioactive material in total (i.e. in the body and outside) will be but it depends how the body excretes it. If the body's excretion is exponential too, then after 1 hour, there will be half left in the body (i.e. ).... I really don't know at all. It is a tricky one!
browsing wiki;

assuming it is exponential, effective half life of two exponential process' is given by

equally for 3 it'd be

so yeah, you're right it's 1 hour, interesting though
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9 years ago
#375
the 2007 maths q12 is annoyinging me. i ended up using chain rule to try dif my equation for the area which resulted in an horific equation. anybody care to post a nice worked method for it?
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9 years ago
#376
(Original post by Bojo)
the 2007 maths q12 is annoyinging me. i ended up using chain rule to try dif my equation for the area which resulted in an horific equation. anybody care to post a nice worked method for it?
you have to use the chain method, check your calculations, you should come out with a nice answer
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9 years ago
#377

If you look hard enough you can see my copy of QED. If you look ULTRA hard you can see some of my physics A2 textbook.

And some of my foot.

I don't usually write out the steps i use when applying the chain rule. I'm pretty sure you can take it from there

(Original post by blueJ-)
you have to use the chain method, check your calculations, you should come out with a nice answer
hmmmm I'm starting to think I shouldn't post worked solutions, I read somwhere that we shouldn't, better to push someone in the right direction. Like you always do.
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9 years ago
#378
still a wee bit fishy to me. i ended up with three answers(ish) one of which was 1/4 - although i see you''ve used the product rule. i might give that a go
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9 years ago
#379
can someone please help me and show me how you get an anwers for 2007 phyics question 9
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9 years ago
#380
(Original post by Bojo)
still a wee bit fishy to me. i ended up with three answers(ish) one of which was 1/4 - although i see you''ve used the product rule. i might give that a go
I don't trust it much either, because I expected a value of 0.5 as well as the two I got.

i was expecting that you get x=0.25, 0.333333333333333333333333333333 333333333333 and 0.5

Two are minima, and one is a maximum. Showing the nature of the point is something i'm never bothered to do.
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