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Question
Math
Posted 10 months ago
Compute the volume of the solid obtained by rotating the region bounded by y=x2y = x^2, x=0x = 0, and y=4y = 4 about the y-axis.
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Answer from Sia
Posted 10 months ago
Solution by Steps
step 1
To find the volume of the solid obtained by rotating the region bounded by y=x2y = x^2, x=0x = 0, and y=4y = 4 about the y-axis, we use the method of disks or washers
step 2
The volume VV of the solid of revolution about the y-axis is given by the integral V=abπr2dyV = \int_{a}^{b} \pi r^2 dy, where rr is the radius of a disk at a given yy and [a,b][a, b] is the interval for yy
step 3
Since y=x2y = x^2, we solve for xx to find the radius: x=yx = \sqrt{y}. Thus, the radius of the disk is r=yr = \sqrt{y}
step 4
The limits of integration are from y=0y = 0 to y=4y = 4 because the region is bounded by y=4y = 4
step 5
The volume integral becomes V=04π(y)2dy=04πydyV = \int_{0}^{4} \pi (\sqrt{y})^2 dy = \int_{0}^{4} \pi y dy
step 6
Integrating πy\pi y with respect to yy from 0 to 4, we get V=[πy22]04V = \left[\frac{\pi y^2}{2}\right]_0^4
step 7
Evaluating the integral, we find V=π422π022=16π2=8πV = \frac{\pi 4^2}{2} - \frac{\pi 0^2}{2} = \frac{16\pi}{2} = 8\pi
Answer
The volume of the solid is 8π8\pi cubic units.
Key Concept
Volume of a solid of revolution using the disk method
Explanation
The volume is found by integrating the area of circular disks, which are formed by rotating the region about the y-axis. The radius of each disk is given by the function describing the boundary of the region, in this case, y=x2y = x^2.

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