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Thread: HSC Physics Marathon 2013-2015 Archive

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    Senior Member Magical Kebab's Avatar
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    HSC Physics Marathon 2013-2015 Archive

    The HSC Physics Marathon is an open chain of questions between students. It works by answering a question then posting another question and allowing the cycle to repeat itself.

    Rules:
    - After answering a question, always provide a new one - this is what keeps the thread alive.
    - Allocate a number of marks for any question that you post.
    - Do not cheat, if you cannot answer a question, do not search how to answer the question but rather, allow other students to answer the question.
    - No copyrighted questions (eg CSSA and Independent) should be posted.

    Tips:
    - It may help to write your answers on paper before typing them on this thread as it will mirror your exam.
    - You may post more than one question.
    - When possible, after questions have been answered, you can peer mark using the marking scheme.

    EDIT:

    This thread is an archive for the questions from older years.

    Feel free to post in the marathon thread for the current HSC year about anything in this thread. Make sure to quote what you are inquiring about!
    Last edited by anomalousdecay; 7 Dec 2014 at 9:34 PM.

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    Executive Member bleakarcher's Avatar
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    Re: 2013 HSC physics marathon

    lol, chemistry died.
    Physics is to mathematics like sex is to masturbation.” —Richard Feynman

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    Senior Member Magical Kebab's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by bleakarcher View Post
    lol, chemistry died.
    Try answer my question

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    Member Immortalp00n's Avatar
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    Re: 2013 HSC physics marathon

    Special precautions must be made when a spacecraft returns to the Earth's atmosphere. Discuss what precautions must be taken to ensure that a manned spacecraft safely returns to Earth. ( 3 marks)
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    Junior Member Currybear's Avatar
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    Re: 2013 HSC physics marathon

    which year which question?
    HSC 2013

    3U Math 1/14 | 4U math 1/2 | Physics 2/16 |Economics 5/19 | Advanced Eng 31/71 |

    Aim >95
    Uni : possibly commerce/ economics at unsw or commerce/it perhaps even engineering tbh got no clue

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    Executive Member bleakarcher's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by Magical Kebab View Post
    Same rules as chemistry.
    Also, try allocate marks and mark the question answered previously and also give feedback etc. be harsh/strict (post HSCers).

    Explain the changes in momentum when a satellite fires its propulsion system (3 marks)
    When a satellite fires its propulsion system, a thrust is generated as a reaction force which arises as a result of the outward force of gases exiting the exhaust when fuel is burnt in the engine. The forces are equal in magnitude by Newton's third law and opposite in direction and so the net momentum of the rocket-fuel system is conserved whereas the momentum of the rocket increases in the direction of thrust.

    I doubt this answer would get all three marks. I cbf right now.
    Last edited by bleakarcher; 5 Jan 2013 at 10:38 PM.
    Physics is to mathematics like sex is to masturbation.” —Richard Feynman

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    Arizona Tears EpikHigh's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by Immortalp00n View Post
    Special precautions must be made when a spacecraft returns to the Earth's atmosphere. Discuss what precautions must be taken to ensure that a manned spacecraft safely returns to Earth. ( 3 marks)
    Is this one reason? Sorry too tired to think properly.

    Entry angle between 7.2 and 5.2 degrees because if the re-entry angle is to shallow the spacecraft will bounce of the atmosphere and due not having excess fuel because of costs they won't have enough fuel to make another re-entry. If the re-entry is to steep then the spacecraft will burn up.

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    Executive Member nightweaver066's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by EpikHigh View Post
    Is this one reason? Sorry too tired to think properly.

    Entry angle between 7.2 and 5.2 degrees because if the re-entry angle is to shallow the spacecraft will bounce of the atmosphere and due not having excess fuel because of costs they won't have enough fuel to make another re-entry. If the re-entry is to steep then the spacecraft will burn up.
    There are lots of precautions

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    Retired Nov '14 someth1ng's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by EpikHigh View Post
    Is this one reason? Sorry too tired to think properly.

    Entry angle between 7.2 and 5.2 degrees because if the re-entry angle is to shallow the spacecraft will bounce of the atmosphere and due not having excess fuel because of costs they won't have enough fuel to make another re-entry. If the re-entry is to steep then the spacecraft will burn up.
    Why/how? (Gas pressure caused by the spacecraft is sufficient to rebound it out of the atmosphere)

    Again, why/how? (If it is too steep, excessive friction will cause too much heat to be produced as gravitational potential energy is lost)
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    Arizona Tears EpikHigh's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by nightweaver066 View Post
    There are lots of precautions
    I know there are lots. What I meant was in my answer one of those reason wasn't 100% sure really tired.

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    Re: 2013 HSC physics marathon

    5.2 - 7.2 is only for the apollo spacecraft, you'll have to specify that if you want to use that range in your answer
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    Junior Member premskies's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by Immortalp00n View Post
    Special precautions must be made when a spacecraft returns to the Earth's atmosphere. Discuss what precautions must be taken to ensure that a manned spacecraft safely returns to Earth. ( 3 marks)
    Issue: There is an optimum angle for safe re-entry for a manned spacecraft. Failure to meet such an angle can result in fatality and destruction. Further factors that must be taken into consideration and appropriately treated in order for a safe re-entry are acceleration of the spacecraft, g-forces experienced by the spacecraft as well as heat of the spacecraft.

    For Apollo capsules, this angle was between 5.2 and 7.2 degrees, HOWEVER, this would differ for other spacecraft's. If the angle is too shallow, the spacecraft may 'skip' off the atmosphere and go into deep space, as a result of the substantial compression of the atmosphere beneath it. This idea is similar to a rock skipping off a pond.
    If the angle is too steep, the heat of re-entry as well as the consequent g-forces that are produced may be too great to ensure the survival of the spacecraft as well as its occupants.

    Not sure if these points would be required for the 3-marker but some general precautions include:
    - Spacecrafts with a 'blunt nose' produce a shock-wave of air in front of them, which acts to essentially absorb a large proportion of the frictional heat produced.
    - Using "breaking ellipses" thereby lengthening the time over which energy is converted into heat.. so basically energy conversions occur over a longer period of time, minimising the chance of substantial accumulation, which can in turn lead to damage to the space shuttle and its functioning.
    - By reclining the astronaut, such that blood is not forced away from the brain, high g-forces can be better tolerated. A moulded fibreglass couch is used for assistance, in turn supporting the body of the occupant.
    - Also, by slowing the rate of descent, g-forces can be minimised by extending the re-entry.

    Q. Recall the optimum position on Earth and orientation of a launch in order to place a satellite in orbit around the Earth (1 mark).

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    Member nifkeh's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by premskies View Post
    Q. Recall the optimum position on Earth and orientation of a launch in order to place a satellite in orbit around the Earth (1 mark).
    The optimum position for launch should be relatively close to/surrounded by a large ocean and be near the equator to place a satellite in orbit efficiently. The launch site of the ESA in Guyana is currently the most ideal site of launch due to its placing being close to and surrounded by the ocean, and the most close to the equator than compared to NASA or Russia's launch sites.

    Don't know if this is a proper question that will be asked (correct me if needed) Q: Describe the effect of length contraction to an observer.
    Last edited by nifkeh; 6 Jan 2013 at 4:48 PM.
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    Junior Member premskies's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by nifkeh View Post
    The optimum position for launch should be relatively close to/surrounded by a large ocean and be near the equator to place a satellite in orbit efficiently. The launch site of the ESA in Guyana is currently the most ideal site of launch due to its placing being close to and surrounded by the ocean, and the most close to the equator than compared to NASA or Russia's launch sites.
    You also may like to add that launch should be in the direction towards east, taking advantage of Earth's rotational motion (West --> East) for a velocity boost..
    Last edited by premskies; 6 Jan 2013 at 5:00 PM.


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    Member nifkeh's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by premskies View Post
    You also may like to add that launch should be in the direction towards east, taking advantage of Earth's rotational motion (West --> East) for a velocity boost..
    Thanks yeah I didn't really answer the 'orientation' part of the question
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    Junior Member premskies's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by Magical Kebab View Post

    Explain the changes in momentum when a satellite fires its propulsion system (3 marks)
    When a satellite's propulsion system is fired, combustion between the fuel and oxidizer occur (within the propulsion system rockets), creating exhaust gases. The rockets push (applying a force) the exhaust gases back out through exhaust jets. Corresponding to Newton's 3rd Law, the gases exert an equal and opposite push forward on the satellite. Thus, the exhaust gases are given an increased reverse momentum, while the satellite is given an increased forward momentum.

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    Junior Member premskies's Avatar
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    Re: 2013 HSC physics marathon

    Q. Identify a reason postulated for the Null Result given by the MM experiment.

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    Re: 2013 HSC physics marathon

    Quote Originally Posted by premskies View Post
    Q. Identify a reason postulated for the Null Result given by the MM experiment.
    The MM experiment attempted to find the Earth's relative velocity through the use of the aether model however the results suggested that no motion of the Earth relative to the aether which led to scientists of the time to the conclusion that the aether was a flawed idea and it simply did not exist.
    However, the MM experiment didn't actually disprove the existence of an aether model but rather it concluded that the earth's velocity relative to the aether was in-measurable.


    not sure if im addressing the question here tbh, feel free to rip into my response
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    Re: 2013 HSC physics marathon

    New Question:
    Discuss the limitation of currently achievable velocities being too slow for extended space travel.
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    Junior Member premskies's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by Immortalp00n View Post
    The MM experiment attempted to find the Earth's relative velocity through the use of the aether model however the results suggested that no motion of the Earth relative to the aether which led to scientists of the time to the conclusion that the aether was a flawed idea and it simply did not exist.
    However, the MM experiment didn't actually disprove the existence of an aether model but rather it concluded that the earth's velocity relative to the aether was in-measurable.


    not sure if im addressing the question here tbh, feel free to rip into my response
    That's a good effort Immortalp00n.

    I was thinking more along the lines of this as a response:
    A null result is produced when an experiment does not produce the expected result. Reasons postulated for the null result of the MM experiment are;
    - Massive objects can drag the aether along with it, hence Earth being stationary relative to the aether (the aether was being dragged along by Earth).
    - The length in direction of the aether was contracted.

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    Exalted Member deswa1's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by premskies View Post
    Q. Identify a reason postulated for the Null Result given by the MM experiment.
    Quote Originally Posted by Immortalp00n View Post
    The MM experiment attempted to find the Earth's relative velocity through the use of the aether model however the results suggested that no motion of the Earth relative to the aether which led to scientists of the time to the conclusion that the aether was a flawed idea and it simply did not exist.
    However, the MM experiment didn't actually disprove the existence of an aether model but rather it concluded that the earth's velocity relative to the aether was in-measurable.


    not sure if im addressing the question here tbh, feel free to rip into my response
    I don't think you even answered the question. You need to give a reason as to why the null result occured.

    Quote Originally Posted by premskies View Post
    That's a good effort Immortalp00n.

    I was thinking more along the lines of this as a response:
    A null result is produced when an experiment does not produce the expected result. Reasons postulated for the null result of the MM experiment are;
    - Massive objects can drag the aether along with it, hence Earth being stationary relative to the aether (the aether was being dragged along by Earth).
    - The length in direction of the aether was contracted.
    I've never heard of those (they could still be right though). About the first, I thought one of the properties of the aether was that it was an absolute frame of reference, encompassed all space etc. -> the Earth can't 'drag' the aether along. For your second, why would you experience length contraction? This is a relativistic effect.

    Personally, I would answer like this (remembering that this is just an identify question):

    The aether does not exist

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    Junior Member premskies's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by deswa1 View Post
    For your second, why would you experience length contraction? This is a relativistic effect.
    Yeah, scientists could later reason that length contraction wasn't responsible since it was a relativistic effect. However at the time, some people believed that length contraction had occurred in the arm parallel to the direction of motion of the apparatus. Again, its just a postulate so this wasn't thought or believed by many, though it was a valid reason in regards to their understanding of relativity at the time.

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    Re: 2013 HSC physics marathon

    so pretty much the MM experiment sought to measure the earth's velocity relative to the aether however the aether did not exist, yielding a null result???


    new question:
    Discuss the issues associated with safe re entry into the Earth's Atmosphere and the precautions and safety measures taken to overcome said issues.
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    Junior Member premskies's Avatar
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    Re: 2013 HSC physics marathon

    Quote Originally Posted by Immortalp00n View Post
    so pretty much the MM experiment sought to measure the earth's velocity relative to the aether however the aether did not exist, yielding a null result???
    Yeah that's exactly right. Those postulates are just reasons that people suggested as to why the yield result occurred (not factual).

    Quote Originally Posted by Immortalp00n View Post
    new question:
    Discuss the issues associated with safe re entry into the Earth's Atmosphere and the precautions and safety measures taken to overcome said issues.
    How much marks? This could potentially be a 3-4 or 7-8 marker?

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    Re: 2013 HSC physics marathon

    Quote Originally Posted by premskies View Post
    Yeah that's exactly right. Those postulates are just reasons that people suggested as to why the yield result occurred (not factual).



    How much marks? This could potentially be a 3-4 or 7-8 marker?
    okay sweet.

    and i'd say a 6 marker
    coz there are a few issues and many ways to overcome em..
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