# Answer to Question #6702 in Mechanics | Relativity for yah

Question #6702
the pressure inside a 1.0cm radius vessel carrying blood with a speed of 0.50m/s is 5200 Newton/ square meter, while the pressure outside is 3200 Newton/ square meter. to what radius must the vessel be reduced so that the outside pressure is greater than that inside, thus making the vessel close at the constriction?
1
2012-02-21T11:07:53-0500
Let&#039;s find the area of the vessel:

S = 4&pi;r&sup2; = 4&pi;1&sup2; = 4&pi;.

We denote the inside pressure force by Fi and outside pressure force by Fo. When the radius is r=1 the values of these forces are:

Fi = S*5200 = 4&pi;5200 = 20800&pi;,
Fo = S*3200 = 4&pi;3200 = 12800&pi;.

We see that Fi &gt; Fo.

We know that inside pressure force is constant under the volume changes. Let&#039;s denote the new radius of the vessel by R.

Fi = Fo
20800&pi; = 3200*4&pi;R&sup2; ==&gt; R = sqrt(20800/4/3200) = sqrt(1.625) = 1.2747

So, the vessel must expand a bit, then the outside pressure will grow up.

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