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Physics problem again -_-

Discussion in 'MCAT: Medical College Admissions Test' started by byeh2004, Nov 28, 2005.

  1. byeh2004

    byeh2004 Senior Member
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    I'm somewhat baffled at this problem, I'm not quite sure how to start this off. But its really interesting this time, its health related! Could someone point me towards the right direction? Thanks!

    In research in cardiology and exercise physiology, it is often important to know the mass of blood pumped by a person's heart in one stroke. This information can be obtained by means of a ballistocardiograph. The instrument works as follows: The subject lies on a horizontal pallet floating on a film of air. Friction on the pallet is neglibible. Initially, the momentum of the system is zero. When the heart beats, it expels a mass m of blood into the aorta with speed v, and the body and platform move in the opposite direction with speed V. The speed of the blood can be determined independently (for example, by observing an ultrasound Doppler shift). Assume that the blood's speed is 55.0 cm/s in one typical trial. The mass of the subject plus the pallet is 54.0 kg. The pallet moves 5.55 10-5 m in 0.160 s after one heartbeat. Calculate the mass of blood that leaves the heart. Assume that the mass of blood is negligible compared with the total mass of the person. This simplified example illustrates the principle of ballistocardiography, but in practice a more sophisticated model of heart function is used.
     
  2. DrChandy

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    This is a conservation of momentum problem
    Where initially
    [M1(patient+pallet)V1(patient+pallet)]+[m2(blood)v2(blood)]=0kgm/s

    ------------------------------------------

    Using the information provided, first find V1

    ------------------------------------------

    Next, set up
    M1V1=-[m2v2]
    And solve for m2, paying attention to signs
     
  3. Sicilian

    Sicilian Senior Member
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    Serway & Faughn? :)
     
  4. byeh2004

    byeh2004 Senior Member
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    yup.

    the solutions manual is lousy =(

    thanks for the help!
     
  5. byeh2004

    byeh2004 Senior Member
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    A water molecule consists of an oxygen atom with two hydrogen atoms bound to it (Figure P8.34). Suppose the angle between the two bonds is 107°. If the bonds are 0.0950 nm long, where is the center of mass of the molecule? (Take the origin to be the center of the oxygen atom and the x axis to be along the dotted line.)

    [​IMG]

    I know how to set the problem up but what do I use for mass? atomic mass? Thanks!
     
  6. DrBowtie

    DrBowtie Final Countdown
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    Their should be a formula. Something like summing the mass x distance (x) from center over the total mass. You have to do this for the x since the symmetry takes care of the y direction.

    Units don't really mattter since they will cancel out. Just make sure the ratio of mass of hydrogen to mass of oxygen is consistent.
     
  7. DrChandy

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    Atomic mass should suffice.
     
  8. Sicilian

    Sicilian Senior Member
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    Haha. That book was great until chapter 7.
     

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