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:
But this does not give the correct volume. The solution says to use:
I am failing miserably to see how my method is different from theirs? Am I messing up a dimension here?