AP Calculus AB : AP Calculus AB

Study concepts, example questions & explanations for AP Calculus AB

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Example Questions

Example Question #1 : Derivatives

The speed of a car traveling on the highway is given by the following function of time:

Note that

What does this mean?

Possible Answers:

The car's speed is constantly changing at time .

The car takes  seconds to reach its maximum speed.

The car is not accelerating at time .

The car is not moving at time .

The car is not decelerating at time .

Correct answer:

The car is not moving at time .

Explanation:

The function  gives you the car's speed at time . Therefore, the fact that  means that the car's speed is  at time . This is equivalent to saying that the car is not moving at time . We have to take the derivative of  to make claims about the acceleration.

Example Question #3 : Techniques Of Antidifferentiation

A jogger leaves City  at.  His subsequent position, in feet, is given by the function:

,

where  is the time in minutes.

Find the velocity of the jogger at 15 minutes.

Possible Answers:

Correct answer:

Explanation:

To find velocity, one has to use the first derivative of :

.

  

Note the units have to be ft/min.

Example Question #161 : Derivatives

A gun sends a bullet straight up with a launch velocity of 220 ft/s. It reaches a height of s=220t-16t^2 after  seconds. What's the acceleration in of the block after it has been ejected?

Possible Answers:

Correct answer:

Explanation:

Since a=\frac{ds^2}{dt^2}, by differentiating the position function twice, we see that acceleration is constant and . Acceleration, in this case, is gravity, which makes sense that it should be a constant value!

Example Question #162 : Derivatives

The speed of a car traveling on the highway is given by the following function of time:

Consider a second function:

What can we conclude about this second function?

Possible Answers:

It represents the rate at which the speed of the car is changing.

It represents the total distance the car has traveled at time .

 

It represents another way to write the car's speed.

It has no relation to the previous function.

It represents the change in distance over a given time .

Correct answer:

It represents the rate at which the speed of the car is changing.

Explanation:

Notice that the function  is simply the derivative of  with respect to time. To see this, simply use the power rule on each of the two terms. 

Therefore,  is the rate at which the car's speed changes, a quantity called acceleration.

Example Question #1 : Corresponding Characteristics Of Graphs Of ƒ And ƒ'

Find the critical numbers of the function, 

 

 

 

 

 

Possible Answers:

Correct answer:

Explanation:

1) Recall the definition of a critical point: 

The critical points of a function  are defined as points , such that  is in the domain of , and at which the derivative  is either zero or does not exist. The number  is called a critical number of .  

 

2) Differentiate 

 

3) Set to zero and solve for 

The critical numbers are, 

We can also observe that the derivative does not exist at , since the term would be come infinite. However,  is not a critical number because the original function  is not defined at . The original function is infinite at , and therefore  is a vertical asymptote of  as can be seen in its' graph, 

 

  Problem 7 plot

 

 

Further Discussion

In this problem we were asked to obtain the critical numbers. If were were asked to find the critical points, we would simply evaluate the function at the critical numbers to find the corresponding function values and then write them as a set of ordered pairs, 

 

Example Question #2 : Corresponding Characteristics Of Graphs Of ƒ And ƒ'

The function  is a continuous, twice-differentiable functuon defined for all real numbers. 

If the following are true: 

Which function could be ?

Possible Answers:

Correct answer:

Explanation:

To answer this problem we must first interpret our given conditions: 

  •  Implies the function is strictly increasing.
  •  Implies the function is strictly concave down.

We note the only function given which fufills both of these conditions is .

Example Question #3 : Corresponding Characteristics Of Graphs Of ƒ And ƒ'

A jogger leaves City  at .  His subsequent position, in feet, is given by the function:

,

where  is the time in minutes.

Find the acceleration of the jogger at  minutes.

Possible Answers:

Correct answer:

Explanation:

The accelaration is given by the second derivative of the position function:

For the given position function:

,

,

.

Therefore, the acceleration at  minutes is .  Again, note the units must be in .  

Example Question #1 : Applications Of Derivatives

A right triangle has sides of lenght  and  which are both increasing in length over time such that: 

a) Find the rate at which the angle  opposite  is changing with respect to time.  

 

Possible Answers:

Correct answer:

Explanation:

A right triangle has sides of lenght  and  which are both increasing in length over time such that: 

Find the rate at which the angle  opposite  is changing with respect to time.

Quesstion 9 related rates triangle

a) First we need to write an expression for the angle  as a function of . Because the angle is opposite the side  we know that the tangent is simply . Take the inverse of the tangent: 

 

Now we need to differentiate with respect to 

 

Recall the the general derivative for the inverse tangent function is:

 

 

Applying this to our function for , and remembering to use the chain rule, we obtain: 

 

Example Question #1 : Modeling Rates Of Change, Including Related Rates Problems­

Soap is sometimes used to determine the location of leaks in industrial pipes. A perfectly spherical soap bubble is growing at a rate of . What is the rate of change of the surface area of the bubble when the radius of the bubble is ?

Possible Answers:

Correct answer:

Explanation:

To determine the rate of change of the surface area of the spherical bubble, we must relate it to something we do know the rate of change of - the volume. 

The volume of a sphere is given by the following:

The rate of change of the volume is given by the derivative with respect to time:

The derivative was found using the following rules:

We must now solve for the rate of change of the radius at the specified radius, so that we can later solve for the rate of change of surface area:

Next, we must find the surface area and rate of change of the surface area of the sphere the same way as above:

Plugging in the known rate of change of the surface area at the specified radius, and this radius into the rate of surface area change function, we get

Example Question #2 : Modeling Rates Of Change, Including Related Rates Problems­

A pizzeria chef is flattening a circular piece of dough. The surface area of the dough (we are only considering the top of the dough) is increasing at a rate of 0.5 inches/sec. How quickly is the diameter of the pizza changing when the radius of the pizza measures 4 inches?

Possible Answers:

 inches/sec

 inches/sec

 inches/sec

 inches/sec

 inches/sec

Correct answer:

 inches/sec

Explanation:

To find the rate of change of the diameter, we must relate the diameter to something we do know the rate of change of: the surface area.

The surface area of the top side of the pizza dough is given by

The rate of change, then, is found by taking the derivative of the function with respect to time:

Solving for the rate of change of the radius at the given radius, we get

 inches/sec

Now, we relate the diameter to the radius of the pizza dough:

Taking the derivative of both sides with respect to time, we get

Plugging in the known rate of change of the radius at the given radius, we get

 inches/sec

We could have found this directly by writing our surface area formula in terms of diameter, however the process we used is more applicable to problems in which the related rate of change is of something not as easy to manipulate.

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