Astronomy C

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Re: Astronomy C

Post by Name » April 21st, 2019, 11:23 pm

OrigamiPlanet wrote:This problem set from this particular PA finals is really confusing me, problems 80-83. Could someone help me understand what formula or formulas I need to be using for this?

Test link:
https://scioly.org/wiki/images/7/73/Pen ... stions.pdf

Key link:
https://scioly.org/wiki/images/1/12/Ans ... states.pdf

Thanks!
It's kinda weird. I can't figure out how they got the answer to number 80, I tried alotta different weird things, nothing worked. But when I calculated escape velo of the B0 star, it is greater then the original speed, making me think the answer should be never? They probably did something along the line of accelerating the gas (by a factor of 278) due to the gravitational acceleration of the neutron star, I don't know what.
81 assuming you have the answer to 80, set 2.48E16=1/2mv^2, solve for v, and divide by c to get 74%
82, also assuming you have the answer to 80, find rest energy with e=mc^2 and divide 2.48E16 by 9E16 to get 28%
83 I did that your given the energy is 8.5E29 and find mass with e=mc^2 and divide 8.5E29/9E16 to get 9.4E12, but this disagrees with the key that says 3.4E13.

Either the key on this test is wrong on some parts, or I'm being very stupid right now.
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Re: Astronomy C

Post by syo_astro » April 22nd, 2019, 12:34 am

Name wrote: It's kinda weird. I can't figure out how they got the answer to number 80, I tried alotta different weird things, nothing worked. But when I calculated escape velo of the B0 star...They probably did something along the line of accelerating the gas (by a factor of 278) due to the gravitational acceleration of the neutron star, I don't know what...Either the key on this test is wrong on some parts, or I'm being very stupid right now.
Upfront, I find the key is right.

Yeah, this is overcomplicating, but good ideas when you're unsure. Off the top of my head it might not be trivial to show how the gas is accelerated, which I guess one might figure as follows: (work by gravity) = F * dist = mg * dist. Like I said, might require harder math to do that in practice since that value of g there would change with distance. It would be nice to do with plain kinetic energy (1/2 m v^2)...if you knew the velocity of the gas on impact...that would be hard because accelerations and kinematics of swirling things will be hard (though, technically a valid approach). Even then, you'd still have to account for gravitational potential energy. In a way, you intuited this with the gravitational acceleration pulling stuff off the B0 star even though gas may not be able to exceed the escape velocity of the star by itself. Maybe there's an equation for these ideas, but there's other ways to do this.

This might be a bit tricky to those that don't have more solid physics backgrounds. Still doable, of course! You definitely don't want to deal with acceleration, which often makes problems involving energy harder (this is sort of the point of defining energy). I'll hint for now you have to think about conservation of energy, KE, and GPE, but even then you might mess up what you're using for mass and radius (conventions are a pain but useful!).
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Re: Astronomy C

Post by antoine_ego » April 22nd, 2019, 4:15 am

Name wrote:
OrigamiPlanet wrote:This problem set from this particular PA finals is really confusing me, problems 80-83. Could someone help me understand what formula or formulas I need to be using for this?

Test link:
https://scioly.org/wiki/images/7/73/Pen ... stions.pdf

Key link:
https://scioly.org/wiki/images/1/12/Ans ... states.pdf

Thanks!
It's kinda weird. I can't figure out how they got the answer to number 80, I tried alotta different weird things, nothing worked. But when I calculated escape velo of the B0 star, it is greater then the original speed, making me think the answer should be never? They probably did something along the line of accelerating the gas (by a factor of 278) due to the gravitational acceleration of the neutron star, I don't know what.
81 assuming you have the answer to 80, set 2.48E16=1/2mv^2, solve for v, and divide by c to get 74%
82, also assuming you have the answer to 80, find rest energy with e=mc^2 and divide 2.48E16 by 9E16 to get 28%
83 I did that your given the energy is 8.5E29 and find mass with e=mc^2 and divide 8.5E29/9E16 to get 9.4E12, but this disagrees with the key that says 3.4E13.

Either the key on this test is wrong on some parts, or I'm being very stupid right now.
Their answer is correct by my math.

By Conservation of Energy, we know that K_1 + U_1 = K_2 + U_2 where K and U are the kinetic energy and gravitational potential energy respectively. Thus,



note that v_1 = 800,000 m/s, r_1 = 0.227 AU = 4e10 m, m=1kg, M=1.88Msol = 3.7e30kg, so K2 = 2.49e16 J.

A faster way of doing this is recognizing that since we're near the bottom of a potential well, the initial energies are essentially zero, since U_2 has such great magnitude, so K_2=U_2. This yield the same answer.
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Re: Astronomy C

Post by diplodocus » April 22nd, 2019, 9:47 am

I'm being thrown into this event with 5 days until states (counting today). We have bad notes (but we have notes at least...) How do you suggest I prepare for this event?

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Re: Astronomy C

Post by TheMysteriousMapMan » April 22nd, 2019, 10:25 am

diplodocus wrote:I'm being thrown into this event with 5 days until states (counting today). We have bad notes (but we have notes at least...) How do you suggest I prepare for this event?
Hi, Diplodocus!

Math is what really makes the difference for doing well in astronomy. Try and look over the math notes that you have (if you have them). If you don't have them, a good general reference sheet may be found on the wiki here. Especially look at the math that pertains to section C) of the topics on the rule sheet.

Also, make sure you have enough of the of the DSOs (preferably IR, UV, visible) that you can identify them–you can't answer questions if you don't know what it is.
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Re: Astronomy C

Post by EastStroudsburg13 » April 22nd, 2019, 10:50 am

TheMysteriousMapMan wrote:
diplodocus wrote:I'm being thrown into this event with 5 days until states (counting today). We have bad notes (but we have notes at least...) How do you suggest I prepare for this event?
Hi, Diplodocus!

Math is what really makes the difference for doing well in astronomy. Try and look over the math notes that you have (if you have them). If you don't have them, a good general reference sheet may be found on the wiki here. Especially look at the math that pertains to section C) of the topics on the rule sheet.

Also, make sure you have enough of the of the DSOs (preferably IR, UV, visible) that you can identify them–you can't answer questions if you don't know what it is.
I disagree with this, actually. You can learn some of the very basic math early (i.e. parallax, distance modulus, basically what's here) but your focus should be on DSOs and other general information. Most likely, the bulk of points will be on these, and they won't be as time-intensive as the more involved math will be. Only when you have a good conceptual grasp on Astronomy does it become worth it to dive deep into the math in an effort to go from "good" to "great".

If you're competing in PA, I recommend looking at past PA state astronomy tests, as the test will likely follow a similar format: https://scioly.org/wiki/index.php/2019_ ... #Astronomy.
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Re: Astronomy C

Post by TheMysteriousMapMan » April 22nd, 2019, 10:52 am

EastStroudsburg13 wrote:
TheMysteriousMapMan wrote:
diplodocus wrote:I'm being thrown into this event with 5 days until states (counting today). We have bad notes (but we have notes at least...) How do you suggest I prepare for this event?
Hi, Diplodocus!

Math is what really makes the difference for doing well in astronomy. Try and look over the math notes that you have (if you have them). If you don't have them, a good general reference sheet may be found on the wiki here. Especially look at the math that pertains to section C) of the topics on the rule sheet.

Also, make sure you have enough of the of the DSOs (preferably IR, UV, visible) that you can identify them–you can't answer questions if you don't know what it is.
I disagree with this, actually. You can learn some of the very basic math early (i.e. parallax, distance modulus, basically what's here) but your focus should be on DSOs and other general information. Most likely, the bulk of points will be on these, and they won't be as time-intensive as the more involved math will be. Only when you have a good conceptual grasp on Astronomy does it become worth it to dive deep into the math in an effort to go from "good" to "great".

If you're competing in PA, I recommend looking at past PA state astronomy tests, as the test will likely follow a similar format: https://scioly.org/wiki/index.php/2019_ ... #Astronomy.
I guess it just might be my experiences then, East. The tests I have taken have been pretty math heavy, with maybe 1-5 questions about DSOs.

Edit: Grammar.
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Re: Astronomy C

Post by EastStroudsburg13 » April 22nd, 2019, 10:56 am

TheMysteriousMapMan wrote:
EastStroudsburg13 wrote:
TheMysteriousMapMan wrote:
Hi, Diplodocus!

Math is what really makes the difference for doing well in astronomy. Try and look over the math notes that you have (if you have them). If you don't have them, a good general reference sheet may be found on the wiki here. Especially look at the math that pertains to section C) of the topics on the rule sheet.

Also, make sure you have enough of the of the DSOs (preferably IR, UV, visible) that you can identify them–you can't answer questions if you don't know what it is.
I disagree with this, actually. You can learn some of the very basic math early (i.e. parallax, distance modulus, basically what's here) but your focus should be on DSOs and other general information. Most likely, the bulk of points will be on these, and they won't be as time-intensive as the more involved math will be. Only when you have a good conceptual grasp on Astronomy does it become worth it to dive deep into the math in an effort to go from "good" to "great".

If you're competing in PA, I recommend looking at past PA state astronomy tests, as the test will likely follow a similar format: https://scioly.org/wiki/index.php/2019_ ... #Astronomy.
I guess it just might be my experiences then, East. The tests I have taken have been pretty math heavy, with maybe 1-5 questions about DSOs.

Edit: Grammar.
That seems likely, because that strikes me as a rather unusual Astronomy question distribution. I do not see a test on the Test Exchange that shares that distribution, but then again, I haven't done a thorough check so perhaps one is in there (and perhaps syo can provide input due to his greater experience with Michigan).
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Re: Astronomy C

Post by TheMysteriousMapMan » April 22nd, 2019, 11:41 am

EastStroudsburg13 wrote:
TheMysteriousMapMan wrote:
EastStroudsburg13 wrote: I disagree with this, actually. You can learn some of the very basic math early (i.e. parallax, distance modulus, basically what's here) but your focus should be on DSOs and other general information. Most likely, the bulk of points will be on these, and they won't be as time-intensive as the more involved math will be. Only when you have a good conceptual grasp on Astronomy does it become worth it to dive deep into the math in an effort to go from "good" to "great".

If you're competing in PA, I recommend looking at past PA state astronomy tests, as the test will likely follow a similar format: https://scioly.org/wiki/index.php/2019_ ... #Astronomy.
I guess it just might be my experiences then, East. The tests I have taken have been pretty math heavy, with maybe 1-5 questions about DSOs.

Edit: Grammar.
That seems likely, because that strikes me as a rather unusual Astronomy question distribution. I do not see a test on the Test Exchange that shares that distribution, but then again, I haven't done a thorough check so perhaps one is in there (and perhaps syo can provide input due to his greater experience with Michigan).
It also might be that I was not clear–math is what, in my opinion/experience, separates the medalers from the rest–because it requires a little more intuition and knowledge than familiarity with basic DSO facts. Thinking about it again, DSOs might be the best place to start with only five days. While some tests have been mostly DSO/conceptual that I have taken, the distribution of scores on those invite tests (my coach wrote them) has been such that the schools who had prepped with math knowledge were clumped significantly higher than the others.
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Re: Astronomy C

Post by syo_astro » April 22nd, 2019, 12:43 pm

Note: Most you's in this most are just meant colloquially, like to everyone.

In my experience, you can actually do really well on tests either way. Keep in mind I haven't done any strict correlation. But the top medalers I see usually have a solid *overall* grasp of the event. Sometimes if there's more points on the math section people who are better at math win. Sometimes if there are more points on the concepts, people who are more prepared with their DSOs/concepts win.

As for particular states, I'm honestly unsure where MI astro is at right now for the writers. I recall years ago MI had a prof. writing that liked paragraph explanations and some nuclear stuff. In that way, I could see why you (to MapMan) might say math is more important. I've found some different writers (some profs and teachers) that prefer those kinds of tests. That said, even then you'd need to know your stellar evolution basics and vocab, which is not as easy to pull up on the spot as some equations (at least in my opinion). If I had to guess the *majority* of tests ARE mostly made up of conceptual/DSO questions...and people usually mess up a ton of them at that (maybe you'd be surprised). I would say maybe a few more state tests than average involve paragraphs for whatever reason (e.g. maybe a prof writes and thinks that's the way to go). This is mostly guessing keep in mind.

So you really do have to both. It then comes down to: are you better at math or concepts / organizing notes? Are you aiming for a medal or not? How is your partner? What state are you / do people have insights about that state.

I think East was just saying that this person probably wants to get moving, medal or not. So getting a math equation sheet and a few practice examples to work off of for a test goes pretty quickly. On the other hand, the massive amount of info and DSO/concept points will definitely require more time (as MapMan said in the last post).
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