For the life of me I can't figure this out!

Serendipity

Calling all College Students! I'm studying for a physics midterm Friday and while going over the review questions, I come across this question that has me TOTALLY stumped.

It says, "A deuteron is the nucleus of a hydrogen isotope and consists of one proton and one neutron. The plasma of deuterons in a nuclear fusion reactor must be heated to approximately 300 million K. What is the RMS speed of the deuterons? Is this a significant fraction of the speed of light c = 3*10^8 m/s? What would the temperature of the plasma be if the deuterons had an RMS speed equal to 0.10c?"

I started out by trying to find <Vrms>, so if I am doing this correctly, (mv^2)/2 = (3/2)KT so <v^2> = sqrt[(3KT)/m]. But then I am stuck at this point.

ARRGH! If anyone could help me figure this out it would be greatly appreciated!!!

exalted512

I think its False?
-Cody

AsSiMiLaTeD

D + T => He-4 + n

You should write that out just to be a smartass

Serendipity

This is what I did so far:

jdhdiggs

I think you should go kick the teacher square in the nuts and tell him where to shove his useless problems. (Assuming you're not planning on being a nuclear engineer that is)

jdhdiggs

appadv wrote: »

This is what I did so far:

What kind of physics class doesn't use engineering paper?

Yes, definately kick the guy in the junk. What physics class is this anyway?

Bamadude

Edit: I see your picture now. Looks like your on the right track.

I think the second part about temperature at 0.10c would just be mc^2=(3/2)KT.

Serendipity

jdhdiggs wrote: »

What kind of physics class doesn't use engineering paper?

Sorry, I was doing this on the train on scrap paper, so sorry for the poor handwriting.

jdhdiggs

Poor handwriting? WTH, that's 10x better than mine. Just suprised that the paper isn't green with little blue boxes all over it, that's all.

I never had to really do plasma physics so I can't be much help on that front. If this is physics 101, I'm glad I'm not 10 years younger.

Serendipity

Bamadude wrote: »

Edit: I see your picture now. Looks like your on the right track.

I think the second part about temperature at 0.10c would just be mc^2=(3/2)KT.

I'm thinking the same thing too. Looks like I'm on the right track but I can't get an answer.

As per the second part, I think you're right!

mc^2=(3/2)KT makes sense.

Thanks!

Serendipity

Also - for the second problem, would T = [(mv_rms)^2]/(3K) work?

Still haven't figured out the first problem yet.

Bamadude

In your first equation, can you plug in K,m,T?

m = 2.6 x 10^-34 kg ? (not sure about the mass)
K = 1.38 x 10^-23 J/K
T = 300 million K

I get 6911528830 m/s or 6.9x10^9 m/s

Serendipity

Bamadude wrote: »

In your first equation, can you plug in K,m,T?

m = 2.6 x 10^-34 kg ? (not sure about the mass)
K = 1.38 x 10^-23 J/K
T = 300 million K

I get 6911528830 m/s

Let me try that...

Serendipity

Hmm, the answer in the back of the book (this is an odd problem) is 1.9*10^6 m/s.

How in the world they got that is beyond me.

WTF?

Bamadude

The mass was wrong. I used 3.34*10^-27 kg from this source and it came out right.

http://physics.nist.gov/cgi-bin/cuu/Value?md

Serendipity

Thank you SO VERY MUCH!

Now I'm trying to figure out the second part, what is the RMS speed.

Would would T = [(mv_rms)^2]/(3K) even be on the right track? Or am I totally confused...

Bamadude

As long as 0.10c is not considered a significant fraction of the speed of light then you can still use classical mechanics (1/2)mv^2.

T = [m(v_rms^2)]/(3K) Perhaps you mis-typed it, but notice the parentheses around v_rms.

I get 7.3E+10 m/s

RuSsMaN

Check out the big brains on the Polk forum!

All I know is what Paul taught me, one and one and one is three......

capecodder

RuSsMaN wrote: »

, one and one and one is three......

..Got to be good looking 'cause...

Serendipity

Bamadude wrote: »

As long as 0.10c is not considered a significant fraction of the speed of light then you can still use classical mechanics (1/2)mv^2.

T = [m(v_rms^2)]/(3K) Perhaps you mis-typed it, but notice the parentheses around v_rms.

I get 7.3E+10 m/s

Yes, I mis-typed it. Still working on the problem right now, but...

Thanks AGAIN!

Serendipity

Finally figured it out. You're right, you can stil use classical mechanics (1/2)mv^2. Made the problem a whole lot easier and solvable.

pearsall001

Who gives a ****!!! The only important math equation is one your CPA should know. To find a good one, just ask him how much is 2+2? The only correct answer is..."What do you want it to be". Now, that CPA's a keeper!!!!

Serendipity

pearsall001 wrote: »

Who gives a ****!!! The only important math equation is one your CPA should know. To find a good one, just ask him how much is 2+2? The only correct answer is..."What do you want it to be". Now, that CPA's a keeper!!!!

Haha, that's very funny.

To the other guys that helped me solve this problem - again, your help is greatly appreciated.

audiobliss

Wow, that is REALLY neat handwriting. Holy cow if you think that's scrappy. If I could get my scanner working I'd scan a page of my notes...not exaggerating at all, half the time I can't read them. I loaned them to a classmate last fall and she gave them back to me the next class period having not copied them...because she couldn't read them! :eek:

Serendipity

audiobliss wrote: »

Wow, that is REALLY neat handwriting. Holy cow if you think that's scrappy. If I could get my scanner working I'd scan a page of my notes...not exaggerating at all, half the time I can't read them. I loaned them to a classmate last fall and she gave them back to me the next class period having not copied them...because she couldn't read them! :eek:

Wow, if you think that is really neat, that's not even my "good" handwriting. I was doing that problem on the train.

Do you have a picture?

audiobliss

Ok, I took pics with my digital camera.

The first pic is just a random page of notes for my Old Testament class.

The second pic is an example of my 'neat' notes that I take when a classmate isn't there and I know they'll have to copy mine.

audiobliss

Actually, now that I look at it, that first page of notes actually appears to be neater than my typical page of notes.

I should've taken a picture of my notes for American Literature. Holy cow they're a mess! :eek:

Serendipity

I can't even read half of that

Serendipity

AB - here ya go...

Serendipity

as requested

audiobliss

Very neat, d00d.