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Astronomy/Astrophysics Help Please

  1. Dec 10, 2006 #1
    Astronomy/Astrophysics Help Please!!

    Ok I am not gonna lie, and I feel terrible doing this, but I have a take home final for my astronomy class and I cannot get answers for a good deal of the questions, they are all multiple choice also. I really like the subject, but i am having a lot of trouble with this, and my teacher is a genius, he even has a show on Discovery Channel Canada. Anyway, he is allowing us to use what we can to get answers, but I still cannot find a lot of them. I think I have answered 34 out of 45. Anyway, I am not going to even post the questions because I do not want it to seem like I expect you all to answer them, but if anyone is willing to please let me know and I will post them up. I really appreciate any help anyone has to offer I know nobody has to help, but it would be really kind and generous if you did. Thanks in advance.
     
  2. jcsd
  3. Dec 10, 2006 #2

    chroot

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    Feel free to post your questions, but please also include your thoughts, and an explanation of why you're stuck. We will not simply answer the questions, but we can help point you in the right direction.

    - Warren
     
  4. Dec 10, 2006 #3
    Alright that's fine with me. Thanks a lot.

    1) Telescopes are made using mirrors or lenses. Lenses are a bit more problematic compared to mirrors because: A) They bend blue light more than red B) They bend red light more than blue C) Mirrors can focus x-rays D) Actually, lenses are better....I have eliminated B and C, I am almost certain it is A, but not 100%

    2) There is one element which is right at the edge of what can be made from fusion in normally burning stars and what requires the violence of a supernova. It is... A) iron B) Helium C) Uranium D) Hydrogen E) Lithium...I am almost certain it is not Lithium or Uranium...I am leaning towards Iron...I would probably eliminate Helium also,

    3) The time it takes you to fall into a black hole as seen by someone far away: A) is infinite B) Is zero C) Depends on the size of the black hole D) depends on the mass of the black hole....I know they see you falling slower and slower into the black hole, but I am not sure if that means it is infinite or not.

    4) The proportion of light of different colours in blackbody radiation from an object tells you: A) the temp of the object B) chem composition of the object C) How much light the object can absorb D) Both temp and chem composition of the object ...I know for a star the colors can tell you temp. and what it is made of, I am not sure if that applies for blackbody radiation

    5) The earth has dust raining on it all the time from space, coming in pretty much equally from all directions. What do you think should happen to the rate at which it turns based on the extra mass? A) stay the same to conserve angular momentum B) speed up due to extra energy of stuff hitting it C) slow down due to extra mass and the need to conserve angular momentum D) not enough info E) initially slow down then speed up....I am almost positive the answer is C here, not 100% though.

    6) Despite the equivalence principle, gravity and acceleration are not quite exactly the same. The thing that distinguishes real gravity produced by a mass from the gravity-like effects of acceleration, is that gravity: A) can be repulsive B) is independent of distance from a mass C) produces tidal forces...I would almost eliminate C, and I am not feeling B, but I am not certain enough to pick A.

    7) Neutrons could have come from just protons and electrons but would involve the production of: A) more electrons B) positrons C) neutrinos D) gamma rays...Honestly have no idea on this really, but I would probably eliminate B and D

    8) How many photons of red light of wavelength 710nm do you need to get at least as much energy as one of blue light with wavelength 301nm? A) 2 B) 3 C) 1 D) 4 E) 5....Don't know how to work this out at all to be honest..

    9) The dominant force on the scale of an electron's orbit around a proton in a hydrogen atom is: A) the electrostatic force B) gravity C) weak nuclear force D) magnetism E) stron nuclear force ...Leaning towards strong or weak force, would eliminate magnetism and gravity, but not certain...

    Again, thanks for anyone who can help me out here. I understand you have no incentive for helping me, except to be nice and possibly challenging yourselves I guess?:smile: Anyway, I really appreciate any help. Thanks a lot in advance.
     
  5. Dec 10, 2006 #4

    chroot

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    1, 2, and 3 are all correct.

    For 4, consider that blackbody radiation by definition is the continuous radiation emitted by a uniformly hot object. It has no spectral lines.

    5 is correct. Consider that if the rotational inertia of the planet is constant, increasing its mass must also decrease its angular velocity.

    For 6, consider the direction of the force vector due to gravity. Imagine that you have a very, very large, flat laboratory, and you assemble two pendulums, one at either end of the lab. In what direction does each pendulum hang? Are their strings exactly parallel?

    For 7, why don't you look up the definition of beta decay, and figure out what has to happen to convert a proton and electron into a neutron?

    For 8, can you find the formula for the energy contained in a photon of a specific frequency (wavelength)?

    For 9, the strong and weak force are very short-range, and are only applicable inside the nucleus.

    - Warren
     
  6. Dec 10, 2006 #5

    chroot

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    I have deleted Arian's reply, because it gave away answers (some of which, unfortunately, were also wrong!). This is against PF's policies.

    - Warren
     
  7. Dec 10, 2006 #6

    chroot

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    This is why we're here, robertlouis. We just have some restrictions -- for example, giving away complete solutions -- because we wish to educate here, not to facilitate cheating. This is also the reason we require students to post their thoughts and attempts at solutions before we're willing to help.

    - Warren
     
  8. Dec 10, 2006 #7
    Uh oh, any hint at which ones were wrong:biggrin: ? Anyway, thanks a lot for your help, I really appreciate it. And I understand Arian went against forum rules, but I still appreciate his help a lot. Thanks.
     
  9. Dec 10, 2006 #8

    chroot

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    I gave you plenty of hints about the ones you got wrong -- do you understand the hints? Do you need additional help?

    - Warren
     
  10. Dec 10, 2006 #9
    Yea I completely understand I didn't expect anyone to give me full answers without me atleast putting my thoughts or attempting to get it right first. However, I did happen to see Arian's reply before it was deleted and couldn't help myself to some of them. You did say some of his answers were wrong though, so I was wondering if you could hint to which ones:biggrin: . Thanks again.
     
  11. Dec 10, 2006 #10

    chroot

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    If you're not willing to invest the time in actually learning the material, I'm not going to invest the time in trying to guide you to the answers.

    - Warren
     
  12. Dec 10, 2006 #11
    I am sorry maybe there is a misunderstanding. I have no problem in trying to learn the material, I even looked up everything you told me and found one or two answers. However, being that my paper is due tomorrow and I have another final exam to study for, I do not have too much time so I actually took some of Arian's answers that were posted up. I honestly do not know who would not have in my situation. Anyway, thanks for any help again. Sorry if there was a misunderstanding.
     
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