# AP Calculus AB : Finding specific antiderivatives using initial conditions, including applications to motion along a line

## Example Questions

### Example Question #1 : Finding Specific Antiderivatives Using Initial Conditions, Including Applications To Motion Along A Line

A particle is moving in a straight path with a constant initial velocity. The particle is then subjected to a force causing a time-dependent acceleration given as a function of time:

After 10 seconds, the particle has a velocity equal to  meters-per-second. Find the initial velocity in terms of the constants ,   and

Units are all in S.I. (meters, seconds, meters-per-second, etc.)

Explanation:

Begin by finding the velocity function by integrating the acceleration function.

We use  as the constant of integration since the function  is a velocity and at initially, at , the velocity is equals the constant of integration.

At  seconds we are told the velocity is equal to

### Example Question #2 : Finding Specific Antiderivatives Using Initial Conditions, Including Applications To Motion Along A Line

Find the average value of the function  on the interval

Explanation:

The average value of a function on a given interval  is given by the following function:

Now, let's simply input our values and function in:

### Example Question #3 : Finding Specific Antiderivatives Using Initial Conditions, Including Applications To Motion Along A Line

Determine the position function for a particle whose velocity is given by the equation

and whose initial position is 10.

Explanation:

The position function describing any object is the antiderivative of the velocity function (in other words, velocity is the derivative of position).

So, we first integrate the velocity function:

The following rule was used for integration:

Now, to determine the constant of integration, we use our initial condition given,

Plugging this into our function, we get

### Example Question #4 : Finding Specific Antiderivatives Using Initial Conditions, Including Applications To Motion Along A Line

The function describing the acceleration of a spacecraft with respect to time is

Determine the function describing the position of a spacecraft given that the initial acceleration is 0, the initial velocity is 3, and the initial position is 9.

Explanation:

To find the position function from the acceleration function, we integrate the acceleration function to find the velocity function, and integrate again to get the position function:

The integral was found using the following rule:

To find the constant of integration, we use the initial velocity condition given:

Now, after replacing C with the known value, we integrate the velocity function to get the position function:

The same rule of integration was used as above.

We use the same procedure to solve for C, too, only this time using the initial position condition:

### Example Question #5 : Finding Specific Antiderivatives Using Initial Conditions, Including Applications To Motion Along A Line

Given a particle with an acceleration at time  to be  . With initial conditions  and  where  is the velocity at time , and  is position of the particle at time .

Find the position at time .

Explanation:

We first must establish the following relationship

and

We now may note that

or

Since

We must plug in our initial condition

Therefore our new velocity equation is

We now may similarly integrate the velocity equation to find position.

Plugging in our second initial condition

We find our final equation to be:

### Example Question #1 : Finding Specific Antiderivatives Using Initial Conditions, Including Applications To Motion Along A Line

Find the velocity function given the following information:

The acceleration function is  ;

Explanation:

To find the velocity function, we integrate the acceleration function (the acceleration is the antiderivative of the velocity):

The rules of integration used were

To solve for the integration constant, we plug in the given initial condition:

### Example Question #7 : Finding Specific Antiderivatives Using Initial Conditions, Including Applications To Motion Along A Line

What is the position function if the initial position is 0 and the velocity function is given by

Explanation:

To find the position function, we must integrate the velocity function, as velocity is the antiderivative of position:

The following rule of integration was used:

Finally, we use the initial condition to solve for the integration constant:

### Example Question #1 : Finding Specific Antiderivatives Using Initial Conditions, Including Applications To Motion Along A Line

A particle at the origin has an initial velocity of  . If its acceleration is given by , find the position of the particle after 1 second.

Explanation:

In this problem, letting  denote the position of the particle and  denote the velocity, we know that . Integrating and working backwards we have,

Plugging in our initial condition, , we see immediately that .

Repeating the process again for , we find that

Plugging in our initial condition,  (we started at the origin) we see that . This gives us a final equation

. The problem asks for  which is simply

### Example Question #1 : Finding Specific Antiderivatives Using Initial Conditions, Including Applications To Motion Along A Line

Find the integral which satisfies the specific conditions of

Explanation:

Find the integral which satisfies the specific conditions of

To do this problem, we need to recall that integrals are also called anti-derivatives. This means that we can calculate integrals by reversing our integration rules.

Furthermore, to find the specific answer using initial conditions, we need to find our "c" at the end.

Thus, we can have the following rules.

Using these rules, we can find our answer:

Will become:

And so our anti-derivative is:

Now, let's find c. First set our above expression equal to y

Next, plug in   for y and t. Then solve for c

Looks a bit messy, but we can clean it up to get:

Now, to solve, simply replace c with 12.12