Calculus
posted by Anonymous on .
A ball of radius 12 has a round hole of radius 6 drilled through its center. Find the volume of the resulting solid.
I tried finding the volume of the sphere and the volume of the cyclinder then subtract however that did not work.

the part that is cut out,what you call a "cylinder" is not really at cylinder.
you are forgetting about the caps on each end of your 'cylinder'
we will have to use Calculus to do that
Visualize a circle, centre at the origin and radius of 12,rotating about the xaxis resulting in our sphere.
NOw visualize a drill bit of radius 3 as the xaxis, drilling out a hole.
volume of sphere = (4/3)pi(12)^3 = 7238.229
(you probably got that)
now the 'cylinder will cut at (√135,3)and (√135,3)
so the volume of the cylinder with flat tops = pi(3)^2(2(√135)) = 1642.59
( I am going to assume you got an answer of 7238.2291642.59 = 5595.639)
I will calculate one of the "caps", then subtract twice that from the above answer.
vol. of cap = pi[integral](144x^2)dx from √135 to 12
= pi[144x  (1/3)x^3│ from √135 to 12
= 5.4159
CHECK MY ARITHMETIC, THIS IS WHERE I USUALLY SCREW UP
so total volume
= 7238.229  1642.59  2(5.4159
= 5584.8072 
ARRGGGHH! ARITHMETIC ERROR!!
<< so the volume of the cylinder with flat tops = pi(3)^2(2(√135)) = 1642.59 >>
should have said:
so the volume of the cylinder with flat tops = pi(3)^2(2(√135)) = 657.036
and then
<<( I am going to assume you got an answer of 7238.2291642.59 = 5595.639) >>
should say:
( I am going to assume you got an answer of 7238.229657.036 = 6581.19
and finally at the end
<< so total volume
= 7238.229  1642.59  2(5.4159
= 5584.8072 >>
should say:
so total volume
= 7238.229  657.036  2(5.4159
= 6570.36