Hydrostatics Problem (Why is this Wrong?)

  • #1
3,003
6
Picture1-32.png


In calculating the vertical force component, you want to find the weight of the missing water.

This should be simple: Find the Volume of the missing water and multiply by specific weight.

Why is my volume calculation incorrect? I am using the volume of the rectangular prism whose top coincides with the surface and whose base coincides with B. Then I subtract the volume of the quarter cylinder:

[tex]V_{Tot}=V_{rect}-.25V_{cyl}[/tex]

[tex]V_{rect}=(1.5+0.75)(0.75)(1.2)[/tex]

[tex].25*V_{cyl}=.25*(\pi (0.75)^2(1.2)[/tex]

But this does not give the correct volume. The solution says to use:

Picture2-19.png


I am failing miserably to see how my method is different from theirs? Am I messing up a dimension here?
 

Answers and Replies

  • #2
3,003
6
Aaahhhhhhhh!!!!! My brain!!!!!!

Edit: How does what they wrote even make any sense?

The first term has dimensions of m^3 and the second has dimensions of m^2 !

Not to mention, if you put those numbers into your calculator they do not equal what they are saying they equal. WTF
 
Last edited:
  • #3
Doc Al
Mentor
45,377
1,748
It looks like the second term in their solution has a typo: They left off the factor of 1.2m.
 
  • #4
3,003
6
It looks like the second term in their solution has a typo: They left off the factor of 1.2m.

Yeah. I think that makes it equivalent to mine if you tack that on.

Sometimes it does not help to be able to check your answers. :grumpy:
 
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