Volume of a solid using shells

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The discussion focuses on finding the volume of the region bounded by the curves y=x^(1/3) and y=x when rotated about the line y=1. The teacher's solution is 4∏/15, while the student calculated 11∏/210, indicating a discrepancy. A suggestion is made to create a sketch of the solid of revolution to better visualize the problem. The lack of a proper rotation around the line y=1 is identified as a potential source of error in the student's calculations. Visual aids are emphasized as crucial for understanding and solving such volume problems accurately.
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Homework Statement



Find the volume of the region bounded by the curve y=x^(1/3) and y=x rotated about the line y=1.

Homework Equations





The Attempt at a Solution


My teacher's solution is 4∏/15 . I got 11∏/210.

http://imageshack.us/a/img443/426/0zhs.jpg
http://imageshack.us/a/img443/426/0zhs.jpg
Where am I going wrong?
 
Last edited by a moderator:
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Feodalherren said:

Homework Statement



Find the volume of the region bounded by the curve y=x^(1/3) and y=x rotated about the line y=1.

Homework Equations





The Attempt at a Solution


My teacher's solution is 4∏/15 . I got 11∏/210.

http://imageshack.us/a/img443/426/0zhs.jpg
http://imageshack.us/a/img443/426/0zhs.jpg
Where am I going wrong?

You don't have a sketch of the solid of revolution, so I can't tell what you did. However, it looks like you didn't rotate the region around the line y = 1. I find that it's helpful to have a sketch of the solid, at least a cross-section of it, showing the typical volume element.
 
Last edited by a moderator:
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

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