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Newton's law of Motion problem

  • Thread starter ryant14
  • Start date
  • #1
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Homework Statement


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

Homework Equations


a = (vf - vi)/t
Summation of horiontal force (F) = ma

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 :)
 

Answers and Replies

  • #2
Doc Al
Mentor
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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?
 
  • #3
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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.
 
  • #4
2,479
99
I'm very suspicious about the data given.A blood velocity of 4.5m/s? That seems too high.
 
  • #5
5
0
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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