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yrelhan4

  • 2 years ago

A simple U-tube that is open at both ends is partially filled with water (d=1000kg/m^3). now a liquid of density d is poured into left arm. it d of liquid surface in the left does not mix with water. it is observed that height of liquid surface in the left arm is 2cm more than height of water surface in left arm. what is density d of the liquid?

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  1. yrelhan4
    • 2 years ago
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    ok so whenever i have done these kind of problems i have always known length of liquid column in the left arm. but not in this question. so how should i start?

  2. yrelhan4
    • 2 years ago
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    @Mashy

  3. Mashy
    • 2 years ago
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    wait.. lemme read the question properly!! :P

  4. Mashy
    • 2 years ago
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    draw.. first draw.. !!

  5. yrelhan4
    • 2 years ago
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    correction: water surface in the right arm.

  6. Mashy
    • 2 years ago
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    and are you sure its the 2cm more than LEFT arm itself?? so basically its saying the length fo the column of the liquid itself is 2cm :O :O :O!!!!

  7. yrelhan4
    • 2 years ago
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    |dw:1361214865922:dw|

  8. yrelhan4
    • 2 years ago
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    length of column isnt 2cm. in the second question they have asked length of the column.

  9. Mashy
    • 2 years ago
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    |dw:1361214958351:dw|

  10. Mashy
    • 2 years ago
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    does that make sense?

  11. yrelhan4
    • 2 years ago
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    it does. but there is still a constant 'a'. how do i eliminate that? where do i apply the pressure equation?

  12. Mashy
    • 2 years ago
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    wait lemme think :P hey what happens if you apply pressure equation for the UPPER LINE level?? left side is pressure due to atm and 2 cm of liquid right side is pressure due to atm only

  13. yrelhan4
    • 2 years ago
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    :O idk what happens. nice man. you are intelligent. :P

  14. Mashy
    • 2 years ago
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    no.. ther is something wrong.. there is something m missing.. you can't do that.. !! :O

  15. yrelhan4
    • 2 years ago
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    why not?

  16. Mashy
    • 2 years ago
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    what why not?? if you equate them.. you ll get the pressure due to 2cm liquid to be zero!!.. cause patm cancel out on both sides!

  17. yrelhan4
    • 2 years ago
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    hmm. sure. :P

  18. Mashy
    • 2 years ago
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    am i too sleepy!??? i just went to my textbooks.. and you can do that for all problems!! consider at the surface of the liquid in the column which is lower.... !?? tell me ?? whats wrong if we do that ?

  19. yrelhan4
    • 2 years ago
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    |dw:1361216017495:dw|

  20. Mashy
    • 2 years ago
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    not that.. !! |dw:1361216075828:dw|

  21. Mashy
    • 2 years ago
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    you could do that for all problems.. and the density of all liquids would come zero! :-/

  22. yrelhan4
    • 2 years ago
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    i'm sorry. no ideas whats wrong. i have done 5-6 problems like this and i have never seen a the level at the surface of a liquid. why not? i dont know.

  23. Mashy
    • 2 years ago
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    even i dunno!!.. this is insane.. anwyays.. i think you can tke for the lower line ... in that case, the height of the liquid would be a +2... and the height of the water would be just a.. lol.. i dunno if that works :D

  24. Mashy
    • 2 years ago
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    maybe you shouldnt consider at the surface... cause on one side its liquid and the other side its air.. so the pressures really need not be the same!!

  25. Mashy
    • 2 years ago
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    yea that must be it :P

  26. yrelhan4
    • 2 years ago
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    haha. alright. :P

  27. Mashy
    • 2 years ago
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    but still thats not convincing me.. DAMN YOU.. its already 1.15 am here and now i can't sleep!! argggg

  28. rajathsbhat
    • 2 years ago
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    it's simple guys

  29. yrelhan4
    • 2 years ago
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    haha. spend sometime on this question. maybe it'll help you to sleep. :P

  30. Mashy
    • 2 years ago
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    plz rajath.. tel why !!

  31. rajathsbhat
    • 2 years ago
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    dg(a+2)=1000ga. makes sense? refer to mashy's diagram.

  32. Mashy
    • 2 years ago
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    yea but how will you solve that??????? but my question is.. why can't we ever consider at the surface???

  33. yrelhan4
    • 2 years ago
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    lol. how would you eliminate a? another equation? what would it be?

  34. Mashy
    • 2 years ago
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    something is missing in your question.. too ambiguous !! ll post a new question.. wait!!

  35. rajathsbhat
    • 2 years ago
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    ^ikr

  36. yrelhan4
    • 2 years ago
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    well its what the book says. idk,

  37. rajathsbhat
    • 2 years ago
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    ooh i got it. just a sec

  38. Mashy
    • 2 years ago
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    quick.. i need to sleep!! :P

  39. rajathsbhat
    • 2 years ago
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    use the buoyant force equation for the new liquid. you get dgA(a+2)=1000gAa get an equation for d in terms of a and substitute it into the first equation.

  40. rajathsbhat
    • 2 years ago
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    A is the area of cross section of the tube

  41. Mashy
    • 2 years ago
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    doesn't that give you back the same equation!?!? :P

  42. rajathsbhat
    • 2 years ago
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    lolol i just realized that xD

  43. yrelhan4
    • 2 years ago
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    lol. it does. :P

  44. Mashy
    • 2 years ago
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    you are just running in circles.. omg.. our smartscores are at the stake here rajath's being the most LOLZZ :D

  45. rajathsbhat
    • 2 years ago
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    hey but there is this one thing. why does it look like the pressure exerted by the 2cm column is 0?

  46. Mashy
    • 2 years ago
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    thats the problem m trying to tackle from that time.. if you consider pressure equation at the surface.. every problem gives you answer as zero.. something is horribly wrong with logic.. check my question.. its at the top!!

  47. yrelhan4
    • 2 years ago
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    ^ that is what mashy is being mad about.

  48. rajathsbhat
    • 2 years ago
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    lol mashy i know i have to brush up on my skillzzzz :P but i'm not letting this one go

  49. yrelhan4
    • 2 years ago
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    thats the spirit :P

  50. yrelhan4
    • 2 years ago
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    @Vincent-Lyon.Fr

  51. Mashy
    • 2 years ago
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    You calling in heavy reinforcements i see :D

  52. Mashy
    • 2 years ago
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    dude.. i seriously believe the question does not give enough data!!.. try thinking practically!!!.

  53. yrelhan4
    • 2 years ago
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    hmm maybe. i think i'll let this one go. :P

  54. rajathsbhat
    • 2 years ago
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    yeah something tells me that 'a' should've been given. But the way this problem is sentenced makes me think otherwise.

  55. Mashy
    • 2 years ago
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    i am more worried about what i was addressing lolzzz..!!! but i think the solution to my problem is.. that you cannot use pressure equation at that level, the surface or any level above that.. cause unlike liquids.. we don't have an equation for the pressure due to atmosphere for a depth !!.. so maybe its forbidden..!! but i really need a better answer !!

  56. yrelhan4
    • 2 years ago
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    anyway, i'm gonna go now. you guys scratch your brains. :P

  57. Mashy
    • 2 years ago
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    no m leaving as well.. thanks for dragging me into this.. really.. now i have something to think about.. so ll give you a medal :D and i ll fan yu :D

  58. rajathsbhat
    • 2 years ago
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    i got it! i know why we can't say that the pressure due to the 2cm is not 0.

  59. Mashy
    • 2 years ago
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    you mean what we can't say that the pressure due to 2cm IS zero?

  60. rajathsbhat
    • 2 years ago
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    yes

  61. Mashy
    • 2 years ago
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    dazzle me .. quick quick!!!

  62. Mashy
    • 2 years ago
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    did you fall asleep or something?!?!?

  63. rajathsbhat
    • 2 years ago
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    lmao ok think of the whole liquid column as a solid. the 2cm column is like the part of an iceberg that sticks out of the water surface. it's being held up and not allowed to sink beyond that level because the part of the same liquid below it is applying a force equal to it's weight.

  64. rajathsbhat
    • 2 years ago
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    and how does this solve the problem of pressure you ask. I'll tell you how.

  65. rajathsbhat
    • 2 years ago
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    didn't we learn that the molecules inside a liquid are pulled equally by the other molecules? (i remember learning this while learning about surface tension) so, AT THAT LEVEL and AT EVERY LEVEL IN THAT MYSTERY LIQUID, the pressure is the same and it's equal to the atmospheric pressure.

  66. Mashy
    • 2 years ago
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    wait wait wait.. !!

  67. rajathsbhat
    • 2 years ago
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    I could be COMPLETELY WRONG but lemme think about it a little bit more.

  68. yrelhan4
    • 2 years ago
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    *yawn* goodnight both of you! :P

  69. Mashy
    • 2 years ago
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    first of all you can't treat it like a solid.. cause fluid mechanics doesn't hold good for solid!! :P.. but wait.. m thinking!!

  70. Mashy
    • 2 years ago
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    yrelhan4.. if i ever meet you .. remind me to first kill you :D

  71. Mashy
    • 2 years ago
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    |dw:1361219680403:dw| if what you are saying is true.. (whatever that is :D) if it applies at level 1, why doesn't it apply at level 2?? why isn't level 2 at atm pressure??

  72. Mashy
    • 2 years ago
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    |dw:1361219869615:dw| a better picture :P

  73. rajathsbhat
    • 2 years ago
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    you're right....obviously there is a gap in my understanding of this part of the universe.

  74. Mashy
    • 2 years ago
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    or maybe we found a flaw in mechanics.. quickly lemme patent this.. before you steal away my query :D

  75. rajathsbhat
    • 2 years ago
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    Mark my words - I will get to the bottom of this (if vincent doesn't answer first :P) in less than 24 hours from now. (and lol ^)

  76. Mashy
    • 2 years ago
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    K i really need to sleep now.. so ll go now .. .bye bye.. lets discuss tihs with someone who actually knows physics lol :D !! m ashamed to call myself physics teacher now!

  77. rajathsbhat
    • 2 years ago
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    see ya tomorrow. this is a wake up call for me. Time to whip out those dusty old physics books :P

  78. yrelhan4
    • 2 years ago
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    ok so got it guys. the options are 1000,1200,1400,800 kg/m^3 according to equation dg(a+2)=1000ga, obviously d<1000, so that would mean d=800. so that is that. thank you for wasting your time on this question. :P cheers!

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