John Cuthber

"I'm not sure why you are pressing the issue of putting this in context of the OP" Because I have this weird idea that the OP asked the question because he wanted an answer. Dr Rockets's saying "Conservation of momentum will be a helpful principle in this problem." is, at best unhelpful, because the momentum is unknown and also is, as far as I can see, flat out wrong. I'm happy to see anyone actually show that the statement is true by using momentum as a helpful principle in this problem. But until then, the point remains that, since the problem is not open to solution, neither momentum nor energy nor slaughtering a goat will actually help.

It would be difficult to make such a telescope, but the real problem would be pointing it in the right direction. You would need to track the earth as it moves round the sun (not to mention spinning at 1000 miles an hour at the equator.)

The answer is about 30, provided that you can find a planet where the ambient pressure is 1000 psi. Otherwise it simply won't work.

OK Xitten, if you think Dr Rocket's post saying that momentum helps here is correct then could you use momentum to answer the question? It seems Dr Rocket himself is ignoring the issue in the hope it will go away.

The tragedy of that documentary is the date at the end. Nothing seems to have happened since.

Dr Rocket, either answer the original question using the concept of momentum, or accept that you were wrong in saying that it would help. Then we can get back to your failure to understand the point about current through, and voltage across, a body not being independent; and to your ability to straw-man on the issue such as pretending that humans might be superconductors.

Where?

"This article about whores andfrigid women is my most popular article." Lol again. "In my opinion thereare only 4 personality types from which one (theorist) meets extremely seldom,therefore the person deals mainly only with 3 types of the person. " Lol again. I know people who can show 4 different personality types before lunch.

I have a magnet holding a piece of paper on the door of my fridge. Nothing moves so no work is done. If I had the magnet on the inside of a very cold fridge, I could use a superconducting coil instead of the magnet. There is no need for any power to be dissipated in either case. If an electron or other charged particle were to pass near this magnet it would experience a force but the force is in a direction at right angles to the motion so no work is done and no power is needed. (it's like the fact that I can roll a 1 ton car on a flat road, in principle, without taking any power. In practice there's a bit of friction. It's only if I want to go up hill that I need to do a lot of work.) The only power needed by a superconducting magnet is the power that drives the fridge. The stored energy in a current carrying inductor is 1/2 L I^2 So, since the inductance (L) is not zero, the current has to be finite because the stored energy can't be infinite, but it can be quite large.

"And God said let there be light and let the light ferment." No He didn't.

It's about 8 miles south of Naturita Colorado. And, as far as I can tell, Amateur-1 has discovered farming.

Thing is Jimmy, human sexual behaviour is different from many other animals so the potential risk of infection is different. The other thing is that all embryos demand nutrients from their mothers.

What straw man? You said "Conservation of momentum will be a helpful principle in this problem.". I say it is not . If it helps then give an answer. If you can't do that then momentum didn't really help did it? Exactly what help did it provide? And I understand the physics well enough to not take kindly to your attitude. However I also think that you are mistaken in saying " Nevertheless the fundamental quantity of interest is momentum. " for the simple reason that the momentum is not known. It may have the advantage of being strictly conserved, unlike KE, but you don't know what it is. It is also possible (if you know the distance over which the force acts) to calculate the force directly by appeal to the law of conservation of energy. It won't be absolutely accurate because of losses -that's the effect of a "crumple zone" but it will be close. On the other hand, the point of the crumple is to alter the forces received by the occupants of the car. Force times distance = energy. If you know the energy and the distance, you can calculate the (mean wrt distance) force. Someone already pointed that out. BTW, you can kill someone perfectly well with DC. In any particular case- say a 400 Hz power system on board a 'plane, the impedance is defined (and very largely resistive). The point is that you can not independently change the voltage or the current. There is only one V vs I curve (and it's pretty close to a straight line) Defining one, defines the other. You can't say it was one that killed someone, but not the other. Incidentally, it's horribly complicated, people survive very large power dissipations, provided that the energy is low and they survive relatively large energy shocks provided that the power is low. The point remains that you cannot have volts without amps and vice versa.

There are worse assumptions than that the car comes to a halt. In the UK a collision sould have that effect, if only indirectly. It's true that the OP doesn't ask for an approximation, but it does ask for an answer. There are only really two options "there isn't enough information" or an approximation. There's nothing wrong with approximations and assumptions as long as they are recognised as such. In any event, I'm sure we are all looking forward to Dr Rocket solving the problem by the magic of momentum.

I once read the suggestion that the idea was to shed any pathogenic infection. That makes more sense to me that the idea of an evolutionary battle between the mother and the genetically almost identical embryo.

I'd like to think that the people who set homework questions don't go for the sort of spurious accuracy in the OP. ChemEng, do you know that THF doesn't mix well with salt water?

Alternatively, perhaps he should contact a physician.

I guess it makes a change from crazy people writing in ALL CAPS: this guy seems hardly to use the shift key at all.

Oh yes it can. Iron is a very common impurity in a lot of things- simply because it's rather common. Also FeCl3 is slightly volatile so it can be carried over with the HCl during the manufacture of the acid. If the HCl is concentrated enough it will be yellow but if it's relatively dilute it will be green.

OK, so among the things I doubt is that you actually considered the momentum of the system. It's easy enough to calculate the mass of the car from the velocity and the energy using 1/2 MV^2. But everyone agrees that there is not actually enough information to calculate the force asked for, even if you do calculate the momentum. So, the momentum does not actually help. If you still think I'm wrong then calculate them momentum and solve the problem. To a good approximation, at voltages high enough to kill, the body acts as a simple resistive load. It might not be true in general, but it's true in the particular instance that was defined.

The boric acid can't remember what it was before.

Why do there appear to be iron impurities? I dissolved the stuff in a green (impure) solution of strong HCl,

"The time average of the force (presumably we are talking about the contact force between the car and whatever it hits) is tied to momentum, not energy. " The mass and velocity are probably known. It would certainly be odd not to have a fair idea of the mass. So the relation between energy and momentum is know, so... It's like that absurd idea where people say "it's not the voltage that kills, it's the current." Well, since one is directly proportional to, and not independent of, the other... "Conservation of momentum will be a helpful principle in this problem." I doubt that.

"a force such as a vacuum." What?

The reason for adding the acid (Hydrochloric or sulphuric) is to turn the borax into boric acid. As you already have boric acid you don't need to do that.