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Example Questions
Example Question #191 : How To Find Rate Of Change
If the position of an object at time is represented by the function , when does the object stop moving (i.e. The velocity is zero)?
or
The velocity is never .
When the velocity is , that means . That is, . So .
Example Question #192 : How To Find Rate Of Change
The width of a rectangular prism increases half as fast as its length and a third as fast as its height. How does the rate of change of the prism's volume compare to that of the rate of change of the width when the length, height, and width are equal?
Begin by writing the expression for the volume of a rectangular prism:
The rate of change of the volume can be found by taking the derivative of the equation with respect to time:
Now, we're given some information:
The width of a rectangular prism increases half as fast as its length and a third as fast as its height:
The width when the length, height, and width are equal:
Using this, rewrite the volume equation in terms of width:
The rate of change of the volume is times the rate of change of the rate of change of the width.
Example Question #193 : How To Find Rate Of Change
The width of a rectangular prism increases twice as fast as its length and half as fast as its height. How does the rate of change of the prism's volume compare to that of the rate of change of the width when the width is half the length, which is half the height?
Begin by writing the expression for the volume of a rectangular prism:
The rate of change of the volume can be found by taking the derivative of the equation with respect to time:
Now, we're given some information:
The width of a rectangular prism increases twice as fast as its length and half as fast as its height:
The width is half the length, which is half the height:
Using this, rewrite the volume equation in terms of width:
The rate of change of the volume is times the rate of change of the rate of change of the width.
Example Question #194 : How To Find Rate Of Change
A spherical balloon is deflating, while maintaining its spherical shape. What is the diameter of the sphere at the instance the rate of shrinkage of the volume is equal to the rate of shrinkage of the surface area?
Let's begin by writing the equations for the volume and surface area of a sphere with respect to the sphere's radius:
The rates of change can be found by taking the derivative of each side of the equation with respect to time:
The rate of change of the radius is going to be the same for the sphere. So given our problem conditions, the rate of shrinkage of the volume is equal to the rate of shrinkage of the surface area, let's solve for a radius that satisfies it.
Since the diameter is twice this,
Example Question #195 : How To Find Rate Of Change
A regular tetrahedron is growing in size. What is the height of the tetrahedron at the time the rate of growth of its sides is equal to the rate of growth of its volume?
To tackle this problem, define a regular tetrahedron's dimensions in terms of the length of its sides:
Rates of change can then be found by taking the derivative of each property with respect to time:
The rate of change of the sides isn't going to vary no matter what dimension of the tetrahedron we're considering, so given our problem condition, the rate of growth of its sides is equal to the rate of growth of its volume, solve for the corresponding length of the tetrahedron's sides:
The height of a tetrahedron is given by the equation:
Example Question #196 : How To Find Rate Of Change
A cube is growing in size. What is the length of the sides of the cube at the time that the rate of growth of the cube's surface is equal to 1.5 times the rate of growth of its volume?
Begin by writing the equations for a cube's dimensions. Namely its volume and surface area in terms of the length of its sides:
The rates of change of these can be found by taking the derivative of each side of the equations with respect to time:
Now, solve for the length of the side of the cube to satisfy the problem condition, the rate of growth of the cube's surface is equal to 1.5 times the rate of growth of its volume:
Example Question #197 : How To Find Rate Of Change
A cube is growing in size. What is the length of the sides of the cube at the time that the rate of growth of the cube's volume is equal to twice the rate of growth of its diagonal?
Begin by writing the equations for a cube's dimensions. Namely its volume and diagonal in terms of the length of its sides:
The rates of change of these can be found by taking the derivative of each side of the equations with respect to time:
Now, solve for the length of the side of the cube to satisfy the problem condition, the rate of growth of the cube's volume is equal to twice the rate of growth of its diagonal:
Example Question #198 : How To Find Rate Of Change
A cube is growing in size. What is the area of one of the cube's faces at the time that the rate of growth of the cube's volume is equal to twice the rate of growth of its sides?
Begin by writing the equations for a cube's dimensions. Namely its volume in terms of the length of its sides:
The rates of change of these can be found by taking the derivative of each side of the equations with respect to time:
Now, solve for the length of the side of the cube to satisfy the problem condition, the rate of growth of the cube's volume is equal to twice the rate of growth of its sides
The area of one of those cube's faces is the length of its sides squared:
Example Question #197 : How To Find Rate Of Change
A square is growing in area. What is the length of the square's sides at the moment that the rate of growth of the area is the same as the rate of growth of the square's diagonal?
Start by writing the equations for a square's dimensions.
The rates of change of these can be found by taking the derivative of each side of the equations with respect to time:
Now, solve for the length of the side of the square to satisfy the problem condition, the rate of growth of the area is the same as the rate of growth of the square's diagonal:
Example Question #198 : How To Find Rate Of Change
Use normal rules of differentiation to find the derrivative of the function
Taking the derrivative,
We separate the summed terms:
Using the chain rule:
Simplifying
Now, evaluating at :
which is our answer.
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