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E = - GM m / 2r is the expression for the mechanical energy of the system as you said. It is _always_ true for any object in orbit (physics is not selective). What may not be true is that the mechanical energy is conserved. Forces like friction can subtract energy from E = - GM m / 2r and other...

I'm sorry but what utter crap. The only reason you perceive smoking to be cool is because you have been brainwashed into believing it's cool by hollywood stereotypes (how often does the badass character smoke?). There is nothing cool about inflicting damage upon yourself and those around you.

lol. a delicate balance indeed! must be hard to please you :P

So not true. As for the 5 min problem, my suggestion is if you can't go continuously for that long, just take a break and try something else, have you tried oral?

Your argument doesn't follow using the equation v = (2 pi r)/T. The speed of the object is not some kind of conserved quantity as you suggest. As for v=root[Gm/r]. You cannot use this equation in this circumstance because it is formulated under a different set of assumptions. Namely, that the...

As far as HSC is concerned, yes.

Am I correct in assuming that the projectile is launched horizontally with speed 75 m/s from the edge of a 60 m high cliff? If you want the range, you need to know how long the thing stays airborn, combine this with the fact that it's horizontal speed is unchaning allows you to calculate the...

This equation is wrong. I think what you meant to say was that m1u1 + m2u2 = (m1+m2)v Kinetic energy is not conserved in an inelastic collision, whereas momentum is always conserved.

Hi Roobs, Your answer is correct but I suspect your reasoning is not sound. The earth's surface is rotating, so it is a non-inertial frame of reference. We can't immediately conclude anything about time-dilation due to relative motion without referring to an appropriate inertial...

What do you mean?

L'Université de Paris 7, France.

The girls will hate me for saying this but their attraction to masculanity varies in accord with the menstrual cycle, this is a fact. Basically you can't win, just go metro :)

Wolfowitz, The idiocy of your reply is so inexplicably obvious that any rebuttal of mine is entirely redundant.

Play along, most guys I know aren't smart enough to play hard to get. If he is, you need to reciprocate. If you dive into the deep end and come on really strongly, the results may vary depending on the person. If he REALLY digs you then go for it, otherwise keep on playing or he might lose...

Rebound relationships don't work. what's more they especially suck for the reboundee.

Having just applied for exchange (albeit at another country) I can tell you that the USyd requirement is a credit average over at least 1 year of university study. It goes without saying that better grades will increase the competitiveness of your application. Go talk to the international...

I must say that was one of the worst university cruises I've been on yet. I'm not sure if that says anything about medsci however, coz about 90% of the ppl I talked to were from other degrees (myself included). Anyway, I guess I can't complain since I got the ticket half price. Meh, I'll shut up...

No problem :) Interesting question. Well, from my (limited) understanding of orbital mechanics, the condition for the two bodies to execute a stable orbit is that their total energy is less than zero. In practise you would calculate this as 1/2 m_1 v_1^2 + 1/2 m_2 v_2^2 - G m_1 m_2 / r^2...

It's not actually the engines that cause it to propel back. As Helstar said, the gravitational influence of the planet rotates the velocity vector of the spacecraft relative to the planet into a direction which is aligned with the planetery motion. Since energy is conserved, the speed of the...

pkc, I hardly think it snobbery to point out an obvious fact. The fact is that a correct treatment of inertial frames requires at least some working knowledge of general relativity, or at least flat Minkowski space-time. These topics are usually reserved for honours (4th) year university...