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Physics quiz 2009

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Thread: Physics quiz 2009

  1. #51
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    Default Re: Physics quiz 2009

    Question 2:
    To the first order, the water level in the cup/container would stay constant as the ice melts. So, if you fefer to the water level, you should be able to get out of the question of whether water includes ice or not. However, if you really want to be exact, if you consider the temperature of ice and water initially, and of the total water afterwards, calculate the volume factoring the initial and final temperature, volume change of ice to water, water due to temperature change and the container due to temperature change, it is unlikely the level would stay exactly the same.
    This brings out the point that one needs to know the problem at hand and make the right simplifying assumptions. If you read too much into the problem, you could be in trouble too.

    Question 3:
    "oscillescope" should read as "oscillator" and "piezometer" should be "piezo electric transducer". An oscillescope is a waveform display instrument, an oscillator is a signal generator that can be used to drive a transducer. A transducer is a device that converts one form of energy to another form of energy.

    regards,
    Frank

  2. #52
    Secondary School Student chongkeat's Avatar
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    Default Re: Physics quiz 2009

    Questions like Question 2 have been confusing me for quite a while now.

    I mean, the increase in the level of water when the ice is placed into the water is only equal to the amount of water displaced by the submerged part of the ice, right?

    When the ice melts, won't it have an effect equivalent to me pushing the ice and submerging it completely, i.e. raising the water level?

    But then again, that effect could perhaps be canceled out by the reduction in volume as ice turns into water.....

    I dunno, enlighten me here, please?

  3. #53
    ReCom Addict Administrator youngyew's Avatar
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    Default Re: Physics quiz 2009

    Question 2 is the direct corollary of the Archimedes principle. When the solid ice is floating happily on the water, the volume of the water it displaces is the same as its weight (which is conveniently the same value as its volume using our SI units). Later when the solid ice melts, it turns into water which has the same volume as its weight, and this new water replaces the "hole" where the original submerged ice was. Since the original displaced volume is the same as its weight (= Archimedes principle) which in turn is the volume, the water level will not change.

    Or to make it more concrete:

    Let's assume that in the beginning, x ml of ice is submerged in the water and y ml of ice is above the surface. How much is the weight of the ice? It's x grams (due to Archimedes' principle). When it melts later, there's a "hole" where that x ml of ice used to be. How much water will we get from the molten ice? It's obviously x ml (as the ice's weight is x grams). So you have a "hole" of x ml but it's replaced by x ml of freshly molten water, therefore you get an unchanged water level.

    I have not considered the temperature change that Frank has pointed out with much insight.
    Last edited by youngyew; 08-10-2009 at 11:30 PM. Reason: Automerged Doublepost
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  4. #54
    Secondary School Student eve88's Avatar
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    Default Re: Physics quiz 2009

    gosh, if you're going into temperature changes im going to include effects of evaporation as well....

    okay, since henry keeps asking for ppl to attempt qn 3:

    (disclaimer : im using MCQ-guess reasoning instead of physics as i have *no clue* what hes talking about)

    working in done in order of likelyhood that the assumption is correct.

    1) Background rates, thus answer must always be different. (A is out)
    2) assumption 2 : something changes. thus, something else must change. (B is out)

    C vs D guess. I guess D (flipped a coin)

  5. #55
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    Default Re: Physics quiz 2009

    this Physics quiz 2009 tat u all are discussing, is it the "THE NATIONAL PHYSICS COMPETITION 2009 (NPC 2009)"...??
    Trust in the LORD with all your heart and lean not on your own understanding

  6. #56
    ReCom Staff Wiki Contributor yanno_yamster's Avatar
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    Default Re: Physics quiz 2009

    Quote Originally Posted by Weng View Post
    this Physics quiz 2009 tat u all are discussing, is it the "THE NATIONAL PHYSICS COMPETITION 2009 (NPC 2009)"...??
    Yes, they are.
    Last edited by yanno_yamster; 10-10-2009 at 06:23 PM.
    Do not accept any doctrine from reverence, but first try it as gold is tried by fire.
    -Buddha; in Kalama Sutta-

    May you be well and happy!!! :)

  7. #57
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    Default Re: Physics quiz 2009

    Quote Originally Posted by yanno_yamster View Post
    Yes, they are.
    secondary level..? are the results out yet..?
    Trust in the LORD with all your heart and lean not on your own understanding

  8. #58
    College Student unsolvedcryptex's Avatar
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    Default Re: Physics quiz 2009

    yes the results r out.click the link here.i received my results as well d.so wait till holiday is over.but u cant check wat u get thru the website.onli top 10 r listed


    here
    I'm a great believer in luck, and I find the harder I work, the more I have of it.
    - Thomas Jefferson

  9. #59
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    Default Re: Physics quiz 2009

    Quote Originally Posted by unsolvedcryptex View Post
    yes the results r out.click the link here.i received my results as well d.so wait till holiday is over.but u cant check wat u get thru the website.onli top 10 r listed


    here
    u got top 10...?? how did u receive ur results..??
    Trust in the LORD with all your heart and lean not on your own understanding

  10. #60
    College Student unsolvedcryptex's Avatar
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    Default Re: Physics quiz 2009

    Quote Originally Posted by Weng View Post
    u got top 10...?? how did u receive ur results..??
    eh no la.dun praise me.i din .restless skulmate got.i got very bad results.thats all .so malu to tell my results.

    one monday,actually last monday,my teacher sud went up stage and announced it suddenly.luckily i came and din ponteng.so i received my results on stage.so memalukan when ur results sucked.lolz.jk.at least i can stand with other pro in my skul.
    I'm a great believer in luck, and I find the harder I work, the more I have of it.
    - Thomas Jefferson

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