Question

Find the volume of the solid obtained by rotating the region bounded by the curves \( y = x^{2} \) and \( y = 4 \) about the line \( y = 5 \) using the washer method.

Ask by Mejia May. in Malaysia
Jan 23,2025

Real Tutor Solution

Tutor-Verified Answer

Answer

The volume of the solid is \( \frac{832}{15} \pi \).

Solution

To find the volume of the solid obtained by rotating the region bounded by the curves \( y = x^{2} \) and \( y = 4 \) about the line \( y = 5 \) using the washer method, follow these steps: 1. **Determine the Points of Intersection:** The curves intersect where \( x^2 = 4 \), which gives \( x = \pm 2 \). So, the region of interest is between \( x = -2 \) and \( x = 2 \). 2. **Set Up the Washer Method:** The washer method involves integrating the area of washers (disks with holes) across the interval from \( x = -2 \) to \( x = 2 \). - **Outer Radius (\( R \)):** This is the distance from the line of rotation \( y = 5 \) to the curve \( y = x^2 \): \[ R = 5 - x^2 \] - **Inner Radius (\( r \)):** This is the distance from the line of rotation \( y = 5 \) to the horizontal line \( y = 4 \): \[ r = 5 - 4 = 1 \] - **Volume Integral:** The volume \( V \) is given by: \[ V = \pi \int_{-2}^{2} \left(R^2 - r^2\right) dx = \pi \int_{-2}^{2} \left((5 - x^2)^2 - 1^2\right) dx \] Expanding the integrand: \[ (5 - x^2)^2 - 1 = 25 - 10x^2 + x^4 - 1 = x^4 - 10x^2 + 24 \] So the integral becomes: \[ V = \pi \int_{-2}^{2} \left(x^4 - 10x^2 + 24\right) dx \] 3. **Evaluate the Integral:** Since the integrand is even, we can simplify the computation: \[ V = 2\pi \int_{0}^{2} \left(x^4 - 10x^2 + 24\right) dx \] Integrating term by term: \[ \int_{0}^{2} x^4 dx = \frac{2^5}{5} = \frac{32}{5}, \quad \int_{0}^{2} -10x^2 dx = -10 \cdot \frac{2^3}{3} = -\frac{80}{3}, \quad \int_{0}^{2} 24 dx = 24 \cdot 2 = 48 \] Combining these: \[ V = 2\pi \left(\frac{32}{5} - \frac{80}{3} + 48\right) = 2\pi \left(\frac{96}{15} - \frac{400}{15} + \frac{720}{15}\right) = 2\pi \cdot \frac{416}{15} = \frac{832\pi}{15} \] **Final Answer:** The volume is 832⁄15 multiplied by π. In symbols, Volume = (832 ⁄ 15) · π

Reviewed and approved by the UpStudy tutoring team

error msg
Explain
Simplify this solution

Bonus Knowledge

To find the volume of the solid obtained by rotating the region bounded by the curves \( y = x^2 \) and \( y = 4 \) about the line \( y = 5 \) using the washer method, we start by determining the points of intersection of the curves to find the limits of integration. Setting \( x^2 = 4 \), we solve: \[ x^2 = 4 \implies x = -2 \quad \text{and} \quad x = 2. \] Thus, the region of interest is bounded between \( x = -2 \) and \( x = 2 \). When using the washer method, we identify the outer radius and the inner radius of the washers formed by the rotation around the line \( y = 5 \). - The outer radius \( R(x) \) is the distance from the line \( y = 5 \) to the line \( y = 4 \): \[ R(x) = 5 - 4 = 1. \] - The inner radius \( r(x) \) is the distance from the line \( y = 5 \) to the parabola \( y = x^2 \): \[ r(x) = 5 - x^2. \] The volume \( V \) of the solid of revolution is given by the integral of the difference of the squares of the outer and inner radii: \[ V = \pi \int_{-2}^{2} \left( R(x)^2 - r(x)^2 \right) \, dx. \] Now we compute: \[ R(x)^2 = 1^2 = 1, \] \[ r(x)^2 = (5 - x^2)^2 = 25 - 10x^2 + x^4. \] Thus, the integrand becomes: \[ R(x)^2 - r(x)^2 = 1 - (25 - 10x^2 + x^4) = 1 - 25 + 10x^2 - x^4 = -24 + 10x^2 - x^4. \] Now, we have: \[ V = \pi \int_{-2}^{2} (-24 + 10x^2 - x^4) \, dx. \] To evaluate the integral, we simplify: \[ V = \pi \left( \int_{-2}^{2} -24 \, dx + \int_{-2}^{2} 10x^2 \, dx - \int_{-2}^{2} x^4 \, dx \right). \] Calculating each integral separately: 1. \(\int_{-2}^{2} -24 \, dx = -24 \cdot (2 - (-2)) = -24 \cdot 4 = -96\). 2. \(\int_{-2}^{2} 10x^2 \, dx\): - The function \(10x^2\) is even, so: \[ 2 \cdot \int_{0}^{2} 10x^2 \, dx = 2 \cdot 10 \cdot \left[\frac{x^3}{3}\right]_{0}^{2} = 2 \cdot 10 \cdot \frac{8}{3} = \frac{160}{3}. \] 3. \(\int_{-2}^{2} x^4 \, dx\): - Again, using that it's even: \[ 2 \cdot \int_{0}^{2} x^4 \, dx = 2 \cdot \left[\frac{x^5}{5}\right]_{0}^{2} = 2 \cdot \frac{32}{5} = \frac{64}{5}. \] Putting it all together: \[ V = \pi \left(-96 + \frac{160}{3} - \frac{64}{5}\right). \] Now, we need to combine these fractions, finding a common denominator. The least common multiple of 3 and 5 is 15: \[ -96 = -\frac{1440}{15}, \] \[ \frac{160}{3} = \frac{800}{15}, \] \[ \frac{64}{5} = \frac{192}{15}. \] So now we combine: \[ V = \pi \left(-\frac{1440}{15} + \frac{800}{15} - \frac{192}{15}\right) = \pi \left(-\frac{1440 - 800 - 192}{15}\right) = \pi \

Try Premium now!
Try Premium and ask Thoth AI unlimited math questions now!
Maybe later Go Premium
Study can be a real struggle
Why not UpStudy it?
Select your plan below
Premium

You can enjoy

Start now
  • Step-by-step explanations
  • 24/7 expert live tutors
  • Unlimited number of questions
  • No interruptions
  • Full access to Answer and Solution
  • Full Access to PDF Chat, UpStudy Chat, Browsing Chat
Basic

Totally free but limited

  • Limited Solution
Welcome to UpStudy!
Please sign in to continue the Thoth AI Chat journey
Continue with Email
Or continue with
By clicking “Sign in”, you agree to our Terms of Use & Privacy Policy