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Weird but easy question.

Discussion in 'DAT Discussions' started by gochi, Apr 22, 2007.

  1. gochi

    gochi 10+ Year Member

    1,105
    0
    Nov 24, 2006
    This is a question from the OAT, but I heard the OAT/DAT are similar, since the sample exams have the exact same reading questions and some mc questions aswell.

    If an electron has a mass of 9.709 x 10-31 kg,
    and a proton has a mass of 1.672 x 10-27 kg,
    approximately how many electrons are
    required to have the same mass as one
    proton?

    A. 150,000
    B. 1,800
    C. 5.4 x 104
    D. 5.4 x 10-4
    E. 15 x 10-58


    This is what I did...

    9.709 x 10-31 : 1.672 x 10-27/1.672 x 10-27 = 9.709 x 10-31/1.672 x 10-27 =1

    9.709 x 10-31 - 1.672 x 10-27 = 8.037 x 10-4 ... what am I doing wrong ?
     
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  3. Doogie Howser

    Doogie Howser practicing since age 12 5+ Year Member

    89
    0
    Jan 11, 2006
    mass proton/mass electron. all you need to do is subtract exponents on the 10^x's and divide 9.7/1.67...

    but realistically, you should immediately see that it is going to be some "number x 10^4" and since there is only one answer choice with that, move on
     
  4. gochi

    gochi 10+ Year Member

    1,105
    0
    Nov 24, 2006
    i did, a (10 x 10-31 / 20 x 10-27)= (10/20) x (-31-(-27)= 1/2 x -4...
     
  5. dentstd

    dentstd Fena Gonzales 2+ Year Member

    1,669
    14
    Oct 14, 2006
    [nm. erased]
     
  6. dentstd

    dentstd Fena Gonzales 2+ Year Member

    1,669
    14
    Oct 14, 2006
    But do 1.6E-27 / 9.7 E-31 and you get 1722. Not too too far from 2000.

    Jumping the gun to an answer with 10E4 gives you the wrong answer here.

    But remember which exponent is bigger, 10^-31 or 10^-27. Doogie made that mistake.
     
  7. gochi

    gochi 10+ Year Member

    1,105
    0
    Nov 24, 2006
    If an electron has a mass of 9.709 x 10-31 kg,
    and a proton has a mass of 1.672 x 10-27 kg,
    approximately how many electrons are
    required to have the same mass as one
    proton?

    but we go (mass of electron/mass of proton)... with reference to the exponents -31-(-27)= -4...what the heck ? whats up with this ?
     
  8. dentstd

    dentstd Fena Gonzales 2+ Year Member

    1,669
    14
    Oct 14, 2006
    no, you missed what I said. look at the numbers I used, and the order I used them. which one's on top?

    an electron's smaller. if you divide Me/Mp, then you get a fraction. 1/1722.

    if you divide Mp/Me, you get 1722. (The accepted true number is 1836)
     
  9. Doogie Howser

    Doogie Howser practicing since age 12 5+ Year Member

    89
    0
    Jan 11, 2006
    oh haha whoops....i divided (subtracted) the exponents correctly but not the numbers themselves... silly me, its been a long day.

    i hope i don't make that mistake on thursday :laugh:
     
  10. gochi

    gochi 10+ Year Member

    1,105
    0
    Nov 24, 2006
    Yea, but it does not make sense that way.

    If an electron has a mass of 9.709 x 10-31 kg,
    and a proton has a mass of 1.672 x 10-27 kg,
    approximately how many electrons are
    required to have the same mass as one
    proton?


    "ONE PROTON" means --> (Mp/Mp) : (Me/Mp) --? 1 proton : (Me/Mp)

    but what your saying through your calculations is that...

    (Me/Me) : (Mp/Me) --> 1 electron : (Mp/Me)
     
  11. dentstd

    dentstd Fena Gonzales 2+ Year Member

    1,669
    14
    Oct 14, 2006
    You've overthought this til you've confused yourself. "One proton" means "1 Mp." "Mp/Mp" means "one."

    If you want to think of this algebraically, Me*n=Mp. What is n?

    I don't even know why you did the Mp/Mp, Me/Me shindig. Whatever role that played in your reasoning, discard it. I don't even understand your notation....combo of fractions and ratios?
     

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