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Estimating the force of he water on the dutch boys finger

  • Thread starter Nellen2222
  • Start date
  • #1
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Homework Statement



The little dutch boy saved HOlland by sticking his finger in the leaking dike. if the water level was 2.5m above his finger, estimate the force of the water on his finger


Homework Equations





The Attempt at a Solution



I calculated the pressure on his finger by P = p0+pgh = 125,800 Pa.

But i have no idea what to do now.
 

Answers and Replies

  • #2
172
2
Pressure is Force/Area. You must estimate the area of the boy's finger and use this to convert the pressure to force.
 
  • #3
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how do i do that..
 
  • #4
172
2
how do i do that..
Just look at the units:

[itex]\displaystyle \frac{Force}{Area} × Area = Force[/itex]

To estimate the area of the boy's finger, I would just measure my own finger. Measure the diameter of your finger and approximate it as a circle.
 
  • #5
TSny
Homework Helper
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Nellen2222, Should you use absolute pressure or gauge pressure ρgh? (Edit: forget my question, I was thinking the question was asking what force the boy would need to exert to hold the water back.)
 
Last edited:
  • #6
CWatters
Science Advisor
Homework Helper
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You must estimate the area of the boy's finger and use this to convert the pressure to force.
how do i do that..
Estimate the diameter of his finger. Assume it's circular?
 
  • #7
19,676
3,987
how do i do that..
Assume your finger is approximately a cylinder. Can you guess what the diameter of your finger is? Mine is about 1 cm. But if you can't even estimate that, wrap a string around your finger, and measure its length (after unwrapping it again). Then divide by Pi to get the diameter. Do you know how to get the area of a circle if you know its diameter? Your teacher is not looking for the exact answer, so you don't have to determine the diameter very accurately.
 

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