Sarahisme

acutally i am not so sure maybe it is a) 300/7pi kg.m^2 b) 50/7 N.m

just a quick phys question A wheel mounted on an axis that is not frictionless is initially at rest. A constant external torque of 50 N . m is applied to the wheel for 20 s, giving the wheel an angular velocity of 600 rev/min. The external torque is then re-moved, and the wheel comes to rest 120 s later. Find (a) the moment of inertia of the wheel, and (b) the frictional torque, which is assumed to be constant. and i get (sorry don't have time to write out complete working) a) 60/pi kg.m^2 b) 10 N.m is wrong or right? lol Sarah

we were asked to think about this question in our class today, and i am not entirely sure the answer its to do with enthalphy heat of reactino stuff The question was something like why in the pracs we did involing the neutralisation acedic acid and HCL, was the change in temperature of the HCL greater? my theory, and the keyword here is theory (or mroe correctly wild assumption ) is that..... that stronger acids dissociate more (i have no real basis for this claim, just remember hearing it somewhere), and so there are more breaking of bonds, thus there must be a greater release of energy, resultingn in the greater increase of Temp. in the HCL neutralisation reaction. (i.e. because HCL is a stronger acid than the acedic acid) well anyway, help or advice would be greatly welcommed Sarah

x->-infinity,lim(x+sqrt(x^2-4x+1)) i can't for the life of me work out why or how it is possible the limit is 2?!?!

ok then you there is a 3rd object(an observer)

are you sure? (you probably are right of course, but i am just checking more for myself...) what abot a giant planet with a space ship acclerating or moving towards it, then do you get an increase in KE of the spaceship and thus a slingshot effect?

whats that exactly?

oh ok i mean more a system with 2 objects in it. with a small one and a big one, and you move the smaller one towards the bigger one at a certain velocity (simplified system sort of thing)

lol sorry i missed swansont's post

hmm ok well the situation i was thinking of was a simplified version, that is neither object is rotating (like a planet would for example), so then yeah, what about for that kind of situation?

what about gravitational potential energy?

I was just reading up on the Slingshot effect, and was wondering where the energy comes from for the increased velocity of the "slingshotted" object? Cheers Sarah

but arn't we tring to prove an<=bn? if so, haven't we assumed that to begin with?

ummm i am a bit confused here..... what you first say.... One can easily prove that \lim_{x\to \infty}{g(x)} cannot be \infty or -\infty, and similarly that it cannot be any finite, non-zero value. Thus, the only case that is left is that if the \lim_{x\to \infty}{g(x)} does not exist. seems to contradict (or something like that) what you next say... Thus, assume that \lim_{x\to \infty}{xg(x)}=L, but that \lim_{x\to \infty}{g(x)} does not exist, and find a contradiction, and then you're done. (You should be able to do this part on your own, just go back to the definition of the existence of a limit.) i am of course wrong but i not sure why yet.... lol its just you first say that it is easy to prove that it doesnt exist, and then you say to prove by contradiction by assuming it doesnt exist and then showing it does....??? maybe its just because its late at night, lol and everything makes no sense at this hour....but anyways... night night Dap

yeah i know i tried but i think you have to assume at some point something like that .5<x<1.5 or something? i am not sure?!?! lol

ok, i have to go to bed now, but tomorrow i will have a good think about it, but just reading it then even put a few ideas into my head Thanks Dap

allright cheers Dapthar, that makes sense to me thanks a million (yet again!)

lol i am having more trouble.... there is always 1 or 2 question i can't do and it drives me nuts!!! well the one this time is.... A function g has the property that lim x→∞ xg(x) = L. Prove that lim x→∞ g(x) = 0. i have never done or been shown how to do a proof like this one and i am compltely lost Sarah

hey can anyone help me do this problem? Prove using the formal definition of limit lim x→1 √ x = 1 Thanks and cheers Sarah

Hey all, yet another question Suppose an → a, bn → b and an ≤ bn ultimately. Prove that a ≤ b. i am not sure how to do this.... if anyone has some advice or could show me how, it would be greatly appriciated Sarah

thanks for the offer but i've already got a list... how do you derive it? or more importantly, if i am trying to prove ac=bc or something like that using the axioms, can i just say at a step that a x 0 = 0? like i don't have to give a reason, eg. because of axoim * or something like that?

ok then, lol another question to do with axioms..... is say a x 0 = 0 an axiom or something? because if a x 1 = 1 x a = a is one, i figure a x 0 = 0 has to be some kind of axiom???

?

k thanks

just checking for the x component to start with or should there be a cos theta in there somewhere?