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    (Original post by BPat)
    Anyone done the specimen paper?

    What in the hell is question 10 asking for? I swear its not even gramatically correct.

    Here's the question:

    Lol my class did that one. It looks like another question has been printed on to the end of it. Ignore everything after 'with time'.

    (The answer is C right?)
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    Astrophysics section is giving me trouble with two parts;

    Formation of Stars

    Standard Candles - Just need to confirm what they are. These are stars whose brightness (and thus luminosity) varies with time period. The maximum luminosity is proportional to the time period of variation. So if you can measure the time period of variation of a standard candle you can work out its maximum luminosity directly, right?
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    (Original post by Sasukekun)
    Lol my class did that one. It looks like another question has been printed on to the end of it. Ignore everything after 'with time'.

    (The answer is C right?)
    Yeah, the answer is C.

    I hope they don't make mistakes like that in the real paper. :rolleyes:

    Its so annoying how there aren't any past papers. I hate it!
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    (Original post by BPat)
    Yeah, the answer is C.

    I hope they don't make mistakes like that in the real paper. :rolleyes:

    Its so annoying how there aren't any past papers. I hate it!
    why is it C?
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    (Original post by abstract24)
    why is it C?
    As it gets further away the gravitational field strength decreases, thus the rocket's weight decreases and the resultant force upwards INCREASES. This means the acceleration upwards is increasing over time. So that certainly means;

    - The velocity is definitely not increasing at a constant rate (acceleration is increasing, meaning gradient of velocity/time graph must be increasing) (Thus it's not A)
    - The gradient is definitely not decreasing (as acceleration should be increasing), so it's not B.
    - Velocity is not constant (it's accelerating for one thing) so it's not D.

    As the acceleration is increasing over time, the gradient of the velocity-time graph must be increasing meaning it's C.

    That's the best explanation I got anyway. ;x
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    Can someone explain how energy is released in fission and fusion?
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    (Original post by Sasukekun)
    Astrophysics section is giving me trouble with two parts;

    Formation of Stars

    Standard Candles - Just need to confirm what they are. These are stars whose brightness (and thus luminosity) varies with time period. The maximum luminosity is proportional to the time period of variation. So if you can measure the time period of variation of a standard candle you can work out its maximum luminosity directly, right?
    Standard candles are just the stars of known luminosity.
    These are Cepheid variable stars (the ones for which L varies with T) and Supernova explosions.
    Here.

    What dont you understand in the star formation?
    Those cycles look quite simple, dont they?
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    (Original post by Kameo)
    Can someone explain how energy is released in fission and fusion?
    Both fission and fusion products have higher binding energy per nucleon than the start nuclei.
    This means that they are more tightly bound so there is less mass per nucleon.
    This drop in mass is released as energy.

    From Miles Hudson's book.
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    I've got an exam question to do with pressure and temperature which I have no idea how to approach!

    In July 2003 there was an attempt to fly a manned, spherical balloon to a height of about forty kilometres. At this height the atmospheric pressure is only one thousandth of its value at sea level and the balloon would have expanded to a diameter of 210 m. The temperature at this height is –60 °C. The attempt failed because the thin skin of the balloon split while it was being filled with helium at sea level.

    Make an estimate of the temperature at sea level, and hence obtain the volume of helium the balloon would have contained at sea level if it had been filled successfully.
    (6)

    I don't know where to start! My estimate is that the sea level temperature is 293K but I don't know what to do next! Is this a question that requires conservation of energy?
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    (Original post by yadas)
    Standard candles are just the stars of known luminosity.
    These are Cepheid variable stars (the ones for which L varies with T) and Supernova explosions.
    Here.
    Ok cheers, so Cepheid variable stars are just one form of standard candles. Something that you can work out the Luminosity of directly are known as standard candles. Do Supernovas all have the same Luminosity or something then?

    (Original post by yadas)
    What dont you understand in the star formation?
    Those cycles look quite simple, dont they?
    ...Simple to some I guess. Nevermind.


    Also one last question, I made a pretty picture to illustrate what I mean.



    Obviously it's a simple pendulum, but when we use the cosine formula to work out its displacement at a given time, what is considered as the displacement? Is it the distance A or the distance B?
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    (Original post by Sasukekun)
    Also one last question, I made a pretty picture to illustrate what I mean.



    Obviously it's a simple pendulum, but when we use the cosine formula to work out its displacement at a given time, what is considered as the displacement? Is it the distance A or the distance B?
    Well for that one, you could use the equation to work out the angular displacement if you start at a maximum, where A is the angular amplitude. Provided that theta is small and is in radians, you can use
    to work out the length of the curvature (the arc A).
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    (Original post by Sasukekun)
    Do Supernovas all have the same Luminosity or something then?
    Just as Hodder book says, 'we believe that the maximum luminosity of these exploding stars is the same all over the universe'.

    (Original post by Sasukekun)
    Obviously it's a simple pendulum, but when we use the cosine formula to work out its displacement at a given time, what is considered as the displacement? Is it the distance A or the distance B?
    Well, I never knew myself.
    I think that's a straight line A (not the arc).
    For this reason.
    But the arc looks.. better, as Oliver showed.

    (Original post by OL1V3R)
    I don't know where to start! My estimate is that the sea level temperature is 293K but I don't know what to do next! Is this a question that requires conservation of energy?
    Let's take 1 as the values at sea level and 2 as the values at 40km.
    P1 = 1000*P2
    V2 we can get from the diameter
    T2 we know, and T1 we estimate.
    From gas laws P1V1/T1 = P2V2/T2, and the rest you can do.
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    (Original post by Sasukekun)
    Astrophysics section is giving me trouble with two parts;

    Formation of Stars

    Standard Candles - Just need to confirm what they are. These are stars whose brightness (and thus luminosity) varies with time period. The maximum luminosity is proportional to the time period of variation. So if you can measure the time period of variation of a standard candle you can work out its maximum luminosity directly, right?
    no..those are cepheid variables
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    (Original post by yadas)
    Both fission and fusion products have higher binding energy per nucleon than the start nuclei.
    This means that they are more tightly bound so there is less mass per nucleon.
    This drop in mass is released as energy.

    From Miles Hudson's book.
    What I don't get is, the binding energy is used to fuse the nucleons together, so why is there a release in energy?
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    (Original post by havinghoops)
    Thanks to whoever uploaded all those hundreds of questions on all the topics ! They've been really useful.

    I've been putting them together in a way that means the marks add up to 80, so I sit it like a mock test and get some kind of idea of what I might realistically get. They're just random questions picked out of those documents, so they add up to 80 marks.

    I'll share the rest of them tomorrow if people want more. At school so only have one of them atm.
    That's great! More please if you're happy to.
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    (Original post by Kameo)
    What I don't get is, the binding energy is used to fuse the nucleons together, so why is there a release in energy?
    Because two nuclei are produced in place of 1, meaning that some of the nucleons that were previously fused together in the heavier nucleus, are no longer fused together. As a result not all of the binding energy that was previously available needs to be used, so some of it can be released.
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    (Original post by OL1V3R)
    I've got an exam question to do with pressure and temperature which I have no idea how to approach!

    In July 2003 there was an attempt to fly a manned, spherical balloon to a height of about forty kilometres. At this height the atmospheric pressure is only one thousandth of its value at sea level and the balloon would have expanded to a diameter of 210 m. The temperature at this height is –60 °C. The attempt failed because the thin skin of the balloon split while it was being filled with helium at sea level.

    Make an estimate of the temperature at sea level, and hence obtain the volume of helium the balloon would have contained at sea level if it had been filled successfully.
    (6)

    I don't know where to start! My estimate is that the sea level temperature is 293K but I don't know what to do next! Is this a question that requires conservation of energy?
    Always start my thinking about which variables you have.
    Here you've got T2, an estimate of T1 and V2 (which can be worked out using the diameter). And you know that P2 = P1/1000.

    So, using the ideal gas equation, (P1 x V1) / T1 = ((P1/1000) x V1) / T2.

    Should be easy from there.
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    Damnit, beaten by Yadas.
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    (Original post by The Magnificent KoloToure)
    Always start my thinking about which variables you have.
    Here you've got T2, an estimate of T1 and V2 (which can be worked out using the diameter). And you know that P2 = P1/1000.

    So, using the ideal gas equation, (P1 x V1) / T1 = ((P1/1000) x V1) / T2.

    Should be easy from there.
    What formula is that?
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    (Original post by lefneosan)
    What formula is that?


    I now realise why I couldn't approach the question; because I hadn't remembered that formula! Cheers for reminding me!
 
 
 
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