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Example Questions
Example Question #1 : Volume Of A Solid
A man fills up a cup of water by leaving it outside during a rainstorm. The rate at which the height of the cup changes is equal to . What is the height of water at ? Assume the cup is empty at .
The rate at which the height changes is , which means .
To find the height after nine seconds, we need to integrate to get .
We can multiply both sides by to get and then integrate both sides.
This gives us
.
Since the cup is empty at , so .
This means . No units were given in the problem, so leaving the answer unitless is acceptable.
Example Question #1 : Volume Of A Solid
Approximate the volume of a solid in the first quadrant revolved about the y-axis and bounded by the functions: and . Round the volume to the nearest integer.
Write the washer's method.
Set the equations equal to each other to determine the bounds.
The bounds are from 0 to 3.
Determine the big and small radius. Rewrite the equations so that they are in terms of y.
Set up the integral and solve for the volume.
The volume to the nearest integer is:
Example Question #2 : Volume Of A Solid
Determine the volume of a solid created by rotating the curve and the line by revolving around the -axis.
Write the volume formula for cylindrical shells.
The shell radius is .
The shell height is the function in terms of . Rewrite that equation.
The bounds lie on the y-axis since the thickness variable is . This is from 0 to 1, since the intersection of the line and is at .
Substitute all the values and solve for the volume.
Example Question #1 : Volume Of A Solid
What is the volume of the solid formed when the line is rotated around the -axis from to ?
To rotate a curve around the y-axis, first convert the function so that y is the independent variable by solving for x. This leads to the function .
We'll also need to convert the endpoints of the interval to y-values. Note that when , and when Therefore, the the interval being rotated is from .
The disk method is best in this case. The general formula for the disk method is
, where V is volume, are the endpoints of the interval, and the function being rotated.
Substuting the function and endpoints from the problem at hand leads to the integral
.
To evaluate this integral, you must know the power rule. Recall that the power rule is
.
.
Example Question #6 : Volume Of Cross Sections And Area Of Region
Find the volume of the solid generated when the function
is revolved around the x-axis on the interval .
Hint: Use the method of cylindrical disks.
units cubed
units cubed
units cubed
units cubed
units cubed
The formula for the volume is given as
where and the bounds on the integral come from the interval .
As such,
When taking the integral, we will use the inverse power rule which states
Applying this rule we get
And by the corollary of the First Fundamental Theorem of Calculus
As such,
units cubed
Example Question #1 : Volume Of A Solid
Find the volume V of a solid whose cross section at x is a quarter circle with radius 2x on the interval [0, 3].
To determine the volume of a solid with defined cross sectional areas, the equation
where is the cross sectional area at a given x, and the volume exists on the interval .
Because the cross sectional area is a quarter of a circle with a radius of 2x, we find
The volume is then found with
Example Question #10 : Volume Of A Solid
Let R be the region between the graph of and the x-axis on the interval . Find the volume V of the solid obtained by revolving R about the x-axis.
The volume of solid region rotated around the x-axis such as the one in this problem can be found by summing the area of discs, using the formula :
where f(x) gives the radius of each disk. Applying the equation for this problem:
Example Question #11 : Volume Of A Solid
Let R be the region between f(x) and g(x) on the given interval. FInd the volume V obtained by revolving R around the x-axis.
Interval:
This volume can be found with the washer method, which is done using the equation
where the region to be revolved around the x axis has the upper bound of f(x), the lower bound of g(x), and exists on the interval [a, b]. Applying this equation:
Example Question #12 : Volume Of A Solid
Let R be the region between the function f(x) and g(x) on the interval given below. Find the volume V obtained by revolving R around the y-axis.
Interval:
This volume can be found using the shell method by implementing the formula
Where the region to be rotated about the y-axis is between f(x) and g(x) on the interval .
Additionally, one can notice that here, because f(x)=-g(x), the region between the two function is the same as twice the region betwee f(x) and the x-axis, simplifying our problem. Using this symmetry and the above formula:
Example Question #13 : Volume Of A Solid
Using integration by parts, evaluate the following indefinite integral:
In order to evaluate an integral by parts, utilize the equation:
For the integral given, we can define u and dv:
From this, we can evalute du and v:
Combining these elements usng the equation above, we can begin to evaluate the integral:
The final term of this answer needs to be further, again by integration by parts:
Doing the integration:
Substituting this in back for the previous partial solution:
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