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Example Questions
Example Question #31 : How To Find Rate Of Change
A cup with a shape of an inverted cone that is being filled up with water has a base radius of 3 inches and height 5 inches. If the water is being poured into the cup at a rate of find the rate at which the water level of the cup is rising when the water is 4 inches deep.
Not enough information is given.
To solve this equation, we must first know that the equation for the volume of a cone is
where is the base radius of the cone and is the height of the cone.
We are asked to find the rate of which the water level of the cup changes after the water height in the cone is equal to 4 inches, therefore we take the derivative of the volume equation with respect to time.
To take the derivative of the volume equation, we must use the power rule
as well as the product rule .
The derivative comes out to be
.
We know that
based off of the information given to us in the beginning; now we must just solve for .
Note that different then expected due to the ratio of the cone.
This ratio is
or .
Example Question #1923 : Functions
A spherical snowball stuck into an oven and is melting at a rate such that its volume is decreasing by . When the snowball has a radius of 10 centimeters, how fast is the diameter of the snowball changing? Assume only the surface of the snowball is melting at a uniform rate.
Not enough information is given.
In order to solve this question, we must first know that the volume of a sphere is defined as
.
We are asked to find the rate of which the diameter of the snowball changes when it is melting. Therefore we must take the derivative of the volume equation with respect to time. To do this we will need to utilize the power rule
.
The derivative becomes
and since we know that , we simply plug the variables into the equation and solve for .
However we are asked to find the rate of which the diamater of the snowball changes, therefore we multiply the change of rate of the radius by 2 and obtain that the diameter changes at a rate of .
Example Question #1924 : Functions
A car 40 miles east of point A starts driving north at a rate of 30 miles per hour. What is the rate at which the distance between the car and point A is changing after one hour?
None of the above.
In order to solve this question, we must first see that a triangle is being formed between the car and point A. Therefore a Pythagorean theorem derivative can be used to solve this problem. The Pythagorean therorem
can be derived with respect to time in using the power rule
to obtain
.
We know from the information given to us that
,
therefore simply plugging in and solving for will give us the answer to this problem. However, we must still solve for . can be solved by plugging in the values of and back into the Pythagorean theorem. is equal to 30 miles because after one hour that is how far the car has traveled.
Now we simply plug everything into the derivative equation and solve for
Example Question #1925 : Functions
The seconds hand in the clock shown has a length of five inches. Find the velocity of its tip in the and directions at the depicted moment in time.
For this problem, it will be useful to work in radians. The angle of the secondshand, between the positive x-axis and itself, is given as:
Now, to find the x and y velocities, first write out the form of their positions:
Therefore, their respective velocities are given by their respective derivatives:
The secondshand doesn't change in length, so . As for , that can be found knowing how long it takes the secondshand to complete the circuit around the clock:
Note that movement in the clockwise direction, when dealing with angular motion, is treated as negative.
Knowing this, we can find the velocities:
Example Question #41 : How To Find Rate Of Change
A metal cylinder with a radius of five inches and a height of twenty inches is being heated, causing it to expand. If the radius grows at a rate of and the height grows at a rate of , what is the rate of expansion of the cylinder's volume?
The volume of a cylinder is given by the formula:
wherein represents the cylinder's radius, and its height.
Therefore, to find the rate of expansion, derive each side of the equation with respect to time:
Therefore, for the values given in the problem statement, the rate of expansion of the volume can be found:
Example Question #1925 : Functions
The sides of a right triangle are increasing in length. If the shorter side, which has a length of , increases at a rate of , and the longer side, which has a length of , increases at a rate of , what is the rate of growth of the hypotenuse?
Since this is a right triangle, the hypotenuse can be related to the sides utilizing the pythagorean theorem:
Although the root of each side may be taken, it would be simpler to take the derivative of each side with respect to time as is:
Therefore, the rate of change of the hypotenuse is:
Using the Pythagorean Theorem, the hypotenuse is:
Thus:
Example Question #1 : Comparing Relative Magnitudes (Exponential Growth,Logarithmic Growth, Polynomial Growth)
A cylinder of height and radius is expanding. The radius increases at a rate of and its height increases at a rate of . What is the rate of growth of its surface area?
The surface area of a cylinder is given by the formula:
To find the rate of growth over time, take the derivative of each side with respect to time:
Therefore, the rate of growth of surface area is:
Example Question #44 : How To Find Rate Of Change
Water is being poured into a cylindrical glass at a rate of . If the cylinder has a diameter of and a height of , what is the rate at which the water rises?
The volume equation of a cylinder is
Therefore, the rate of change of each term can be related by taking the derivative of each side of the equation:
Treating the glass as solid, the radius of liquid in it will not change, only the height, so . This simplifies the equation:
Since the radius is half the diameter:
Example Question #45 : How To Find Rate Of Change
The position in meters of a particle after seconds is modeled by the equation
, where .
At what rate, in meters per second, is the position of the particle changing at seconds?
The derivative of a function gives us a new function that describes the rate of change of the original function at every point in its domain. Therefore the derivative of f(t) will produce a new function that describes the rate of change in position with respect to time. Using the product rule, the derivative of f(t) is:
Next substitute 3 for t to find the rate of change of the particle at exactly 3 seconds.
.
Example Question #46 : How To Find Rate Of Change
What is the rate of change of the function
when ?
The find the rate of change of a function at a particular point, find the derivative of the function, then substitute the point into the function. Using the quotient rule, the derivative is:
Next substitute for x.
Now we need to simplify the right hand side.
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