Finding Volume by Integration: Rotating Curves About the y-Axis

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SUMMARY

The volume of the solid formed by rotating the region bounded by the curves y=x³, y=1, and x=0 about the y-axis can be calculated using both the washer and shell methods. For the washer method, the volume is V = (3π/5) when integrating from 0 to 1. The shell method yields a volume of V = (2π/5) using the correct formula 2πx(y_upper - y_lower). It is crucial to use π instead of Ω in the calculations for accurate results.

PREREQUISITES
  • Understanding of calculus concepts, specifically integration.
  • Familiarity with the washer method for volume calculation.
  • Knowledge of the shell method for volume calculation.
  • Ability to interpret and manipulate mathematical expressions involving curves.
NEXT STEPS
  • Study the washer method for volume calculations in more complex scenarios.
  • Explore the shell method in detail, focusing on its applications in different coordinate systems.
  • Practice problems involving rotation of curves about different axes.
  • Review integration techniques, particularly definite integrals in calculus.
USEFUL FOR

Students and educators in calculus, mathematicians, and anyone interested in solid geometry and volume calculations through integration methods.

JJ99
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Find the volume of the solid formed when the region bounded by the curves y=x3, y=1, and x=0 is rotated about the y-axis, use washer AND shell methods

Disc/Washer:
Ωx2dy = Ω(y1/3)2dy = Ωy2/3dy
Volume:
V = 0∫1 Ωy2/3dy = Ω{(3y5/3)/5} = 3Ω/5


Shell:
2Ωy(x)dx = 2Ωx(x3)dx = 2Ωx4dx
Volume:
V = 0∫1 2Ωx4dx = 2Ω{(x5)/5} = 2Ω/5


Obviously this question seems simple enough but I'm finding different answers so I'm going wrong somewhere. Any help is appreciated
 
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JJ99 said:
Find the volume of the solid formed when the region bounded by the curves y=x3, y=1, and x=0 is rotated about the y-axis, use washer AND shell methods

Disc/Washer:
Ωx2dy = Ω(y1/3)2dy = Ωy2/3dy
Volume:
V = 0∫1 Ωy2/3dy = Ω{(3y5/3)/5} = 3Ω/5


Shell:
2Ωy(x)dx = 2Ωx(x3)dx = 2Ωx4dx
Volume:
V = 0∫1 2Ωx4dx = 2Ω{(x5)/5} = 2Ω/5


Obviously this question seems simple enough but I'm finding different answers so I'm going wrong somewhere. Any help is appreciated

For a shell you want ##2\pi x(y_{upper}-y_{lower})## in the integrand. And use ##\pi## instead of ##\Omega##.
 

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