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Minimum force necessary to push out a cork

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


2 arms of a u-tube are not identical, one having twice the diameter of the other. a cork in the narrow arm requires a force of 16n to remove it. the tube is filled with water and the wide arm is fitted with a piston. the min force that must be applied to the piston to push out cork is?


Homework Equations


p=f/a


The Attempt at a Solution


p1=f1/(pi*r^2), p2=f/pi*2r^2, p1=p2, f1/(pi*r^2)=f2/(pi*2r^2)....f2=(pi*r^2)*f1/(pi*r^2) which gives me 32. The answer is actually 64. What am i missing?
 

Answers and Replies

  • #2
tiny-tim
Science Advisor
Homework Helper
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hi drunknfox! :smile:

(have a pi: π and try using the X2 icon just above the Reply box :wink:)
p1=f1/(pi*r^2), p2=f/pi*2r^2, p1=p2, f1/(pi*r^2)=f2/(pi*2r^2)....f2=(pi*r^2)*f1/(pi*r^2) which gives me 32. The answer is actually 64. What am i missing?
it isn't π*2r2 :redface:

(and using a dimensional argument would be much quicker, and less likely to lead to a mistake)
 

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