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Newton's law of Motion problem

  1. Jul 12, 2010 #1
    1. The problem statement, all variables and given/known data
    The lower chamber of the heart, (the left ventricle) pumps blood into aorta. The left ventricular contraction lasts 0.20 seconds, during which time a mass of 88 grams of blood is accelerated from rest to a speed of about 4.5 m/s. Find the acceleration & Force.

    known:
    V final - 4.5 m/s
    V initial - 0 m/s
    Mass - 88 grams or 0.088 kg
    Time it takes for contraction - 0.20 s

    2. Relevant equations
    a = (vf - vi)/t
    Summation of horiontal force (F) = ma

    3. The attempt at a solution

    a = (4.5 m/s - 0 m/s) / 0.20
    = 22.5 m/s^2

    F= ma
    = (0.088kg)(22.5 m/s^2)

    These were my answers but my professor marked it wrong. according to him the acceleration should not exceed than 4.5 m/s^2 and the Force must not be greater than 1 Newton.

    are my interpretations to this problem wrong?

    Is it correct that I've used 0.20 seconds as a time to get the acceleration?

    I am confused about this, "The left ventricular contraction lasts 0.20 seconds, during which time a mass of 88 grams of blood is accelerated from rest to a speed of about 4.5 m/s."

    What does this mean? Is it right that the 88 g of blood obtains 4.5 m/s of final speed at 0.20 seconds or not? Or after 0.20 seconds, the blood starts moving?

    Please help...

    Thanks in advance :)
     
  2. jcsd
  3. Jul 12, 2010 #2

    Doc Al

    User Avatar

    Staff: Mentor

    I don't see anything wrong with your interpretation of the problem or with your solution.

    Did the professor provide a complete solution of his own?
     
  4. Jul 13, 2010 #3
    Yes, my prof has its own solution to this problem but he didn't discuss it in our class. He said this problem may appear in the next test. He just said that no one in his class got it right except his bright student last year.
     
  5. Jul 13, 2010 #4
    I'm very suspicious about the data given.A blood velocity of 4.5m/s? That seems too high.
     
  6. Jul 14, 2010 #5
    Yes, you're right, 4.5 m/s as a final velocity doesn't seems to happen in reality. But this is the velocity stated in this problem.
     
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