Two circle graphs of the same radius of 1 intersect each other's center, and the centers are points & respectively.
If the shaded area is rotated around the -axis to produce an "apple core" structure as shown above, what is the volume of this "apple core"?
Give your answer to the nearest 3 decimal places.
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In order to find the volume of revolution, let us divide the "apple core" into parts by the blue lines y = 2 3 and y = 2 − 3 .
The volume generated between the blue lines (called V 1 ) is bounded by the circle graph on the right: ( x − 1 . 5 ) 2 + y 2 = 1 .
Then x − 1 . 5 = − 1 − y 2 (Note that ( 0 . 5 , 0 ) is on the graph, so the sign must be minus.)
Hence, x 2 = 4 1 3 − 3 1 − y 2 − y 2 .
Then V 1 = ∫ 2 − 3 2 3 π ( x 2 ) d y
= 2 ∫ 0 2 3 π ( 4 1 3 − 3 1 − y 2 − y 2 ) d y
= 2 π [ 4 1 3 y − 2 3 ( a r c s i n ( y ) + y 1 − y 2 ) − 3 y 3 ∣ 0 2 3 ]
= 2 π ( 8 9 ( 3 ) − 2 π )
Now the volume above the blue line is created from the area bounded between the plus & minus signs of the graph: ( x − 0 . 5 ) 2 + y 2 = 1 .
Thus, the rest of the volume = 2 π ∫ 2 3 1 ( 4 5 + 1 − y 2 − y 2 ) − ( 4 5 − 3 1 − y 2 − y 2 ) d y
= 2 π ∫ 2 3 1 2 1 − y 2 d y
= 2 π [ a r c s i n ( y ) + y 1 − y 2 ∣ 2 3 1 ]
= 2 π [ 2 π − ( 3 π + 4 3 ) ]
Adding the parts together, the total volume = 2 π [ 8 7 3 − 3 π ] ≈ 2 . 9 4 3