For the curve \(y=\sqrt{x},\) between \(x=0\) and \(x=2,\) find: The volume of the solid generated when the area is revolved about the \(x\) axis.

Short Answer

Expert verified
The volume is \(2\pi\).

Step by step solution

01

- Understand the Problem

We need to find the volume of the solid formed by revolving the curve defined by the function \(y=\sqrt{x}\) about the \(x\)-axis, within the interval \([0, 2]\).
02

- Set up the Integral for the Volume

The volume \(V\) of a solid of revolution generated by revolving a curve \(y=f(x)\) about the \(x\)-axis from \(x=a\) to \(x=b\) is given by the formula:\[ V = \pi \int_{a}^{b} [f(x)]^2 dx \]For the given problem, \(a=0\), \(b=2\), and \(f(x)=\sqrt{x}\).
03

- Substitute the Function into the Formula

Substitute \(f(x) = \sqrt{x}\) into the integral formula:\[ V = \pi \int_{0}^{2} [\sqrt{x}]^2 dx \]
04

- Simplify the Integral

Simplify the integrand:\[ V = \pi \int_{0}^{2} x \, dx \]
05

- Evaluate the Integral

Evaluate the definite integral:\[ \int_{0}^{2} x \, dx = \left. \frac{x^2}{2} \right|_{0}^{2} = \frac{2^2}{2} - \frac{0^2}{2} = 2 \]
06

- Multiply by \(\pi\)

Finally, multiply the result by \(\pi\):\[ V = \pi \times 2 = 2\pi \]

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

integral calculus
Integral calculus is one of the two main branches of calculus, the other being differential calculus. It focuses on the concept of the integral, which is a mathematical tool used to calculate areas, volumes, and other related quantities. In simpler terms, while differential calculus deals with rates of change (like velocity of a car), integral calculus deals with accumulation of quantities (like distance covered by a car).

Integral calculus is deeply connected with the concept of the antiderivative. An integral essentially 'undoes' what a derivative does. There are two main types of integrals:
  • Indefinite Integral: Represents a family of functions and includes a constant of integration (C).
  • Definite Integral: Represents a number, which usually indicates the area under a curve or the total accumulated quantity.


To understand integral calculus, one must grasp how to set up and evaluate these integrals. This includes knowing how to apply limits, work with infinite sums, and use properties like linearity. Integrals play an essential role in many scientific fields, such as physics, engineering, and economics.
definite integral
A definite integral is a type of integral that calculates the net area under a curve within a specified range. More formally, for a continuous function f(x) on the interval \(a, b\), the definite integral is written as \[ \int_{a}^{b} f(x) \, dx \]

In this exercise, we used a definite integral to find the volume of a solid of revolution. To compute the definite integral, the following steps are typically followed:
  • Set up the integral by determining the limits of integration (from \(a\) to \(b\)).
  • Identify the function to integrate (in this case, \(f(x) = \sqrt{x} \)).
  • Evaluate the integral using proper techniques (substitution, integration by parts, etc.)
  • Compute the limits and subtract to get the net result.


For instance, the net volume of the solid formed by revolving the function \( y = \sqrt{x} \) around the x-axis, across \(x = 0\) to \(x = 2\), was obtained using the definite integral \[ \pi \int_{0}^{2} \left(\sqrt{x}\right)^2 \, dx \]. This integral quantified the collective volume within specified boundaries.
solid of revolution
A solid of revolution is a three-dimensional shape generated by rotating a two-dimensional curve around an axis. This concept is widely used in both mathematics and physics to compute volumes of various objects. When revolving a curve around the x-axis or y-axis, the resulting solid’s volume can be calculated using techniques from integral calculus.

To find the volume of a solid of revolution about the x-axis, the formula used is \[V = \pi \int_{a}^{b} [f(x)]^2 \, dx\]. This formula stems from the idea of summing up infinitely many thin disk volumes, each with radius \(f(x)\) and thickness \(dx\).

This method applies to many different curves and situations. For instance, in our exercise, the curve \(y = \sqrt{x} \) was revolved around the x-axis to form a solid. By integrating its squared value \sqrt{x} \, over the interval from \(x = 0\) to \(x = 2\), we obtained the total volume as \[V = 2 \pi \]

Understanding solids of revolution can be vital in numerous practical applications, ranging from engineering designs to volume-based economic models. It allows us to transform simple curves into complex three-dimensional objects.

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Most popular questions from this chapter

For the curve \(y=\sqrt{x},\) between \(x=0\) and \(x=2,\) find: The mass of a wire bent in the shape of the arc if its density (mass per unit length) is \(\sqrt{x}\).

The following notation is used in the problems: \(M=\) mass, \(\bar{x}, \bar{y}, \bar{z}=\) coordinates of center of mass (or centroid if the density is constant), \(I=\) moment of inertia (about axis stated), \(I_{x}, I_{y}, I_{z}=\) moments of inertia about \(x, y, z\) axes, \(I_{m}=\) moment of inertia (about axis stated) through the center of mass. Note: It is customary to give answers for \(I, I_{m}, I_{x},\) etc., as multiples of \(M\) (for example, \(I=\frac{1}{3} M l^{2}\) ). For the pyramid inclosed by the coordinate planes and the plane \(x+y+z=1\) : (a) Find its volume. (b) Find the coordinates of its centroid. (c) If the density is \(z\), find \(M\) and \(\bar{z}\).

The following notation is used in the problems: \(M=\) mass, \(\bar{x}, \bar{y}, \bar{z}=\) coordinates of center of mass (or centroid if the density is constant), \(I=\) moment of inertia (about axis stated), \(I_{x}, I_{y}, I_{z}=\) moments of inertia about \(x, y, z\) axes, \(I_{m}=\) moment of inertia (about axis stated) through the center of mass. Note: It is customary to give answers for \(I, I_{m}, I_{x},\) etc., as multiples of \(M\) (for example, \(I=\frac{1}{3} M l^{2}\) ). A thin rod \(10 \mathrm{ft}\) long has a density which varies uniformly from 4 to \(24 \mathrm{lb} / \mathrm{ft}\). Find (a) \(M\), (b) \(\bar{x}\), (c) \(I_{m}\) about an axis perpendicular to the rod, (d) \(I\) about an axis perpendicular to the rod passing through the heavy end.

The following notation is used in the problems: \(M=\) mass, \(\bar{x}, \bar{y}, \bar{z}=\) coordinates of center of mass (or centroid if the density is constant), \(I=\) moment of inertia (about axis stated), \(I_{x}, I_{y}, I_{z}=\) moments of inertia about \(x, y, z\) axes, \(I_{m}=\) moment of inertia (about axis stated) through the center of mass. Note: It is customary to give answers for \(I, I_{m}, I_{x},\) etc., as multiples of \(M\) (for example, \(I=\frac{1}{3} M l^{2}\) ). Prove the "parallel axis theorem": The moment of inertia I of a body about a given axis is \(I=I_{m}+M d^{2},\) where \(M\) is the mass of the body, \(I_{m}\) is the moment of inertia of the body about an axis through the center of mass and parallel to the given axis, and \(d\) is the distance between the two axes.

As needed, use a computer to plot graphs and to check values of integrals. Find the centroid of the area above \(y=x^{2}\) and below \(y=c(c > 0)\).

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