Calculus 1 : How to find position

Study concepts, example questions & explanations for Calculus 1

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Example Questions

Example Question #151 : How To Find Position

What is the position function if \displaystyle x(1)=2 when \displaystyle v(t)=3t-1 ?

Possible Answers:

\displaystyle x(t)=\frac{3}{2}t^2-t+2

\displaystyle x(t)=t^2-t+\frac{5}{2}

\displaystyle x(t)=\frac{3}{2}t^2-t-\frac{5}{2}

\displaystyle x(t)=\frac{3}{2}t^2-t+\frac{3}{2}

Correct answer:

\displaystyle x(t)=\frac{3}{2}t^2-t+\frac{3}{2}

Explanation:

To find the position function, you must integrate the velocity function. To integrate, add 1 to the exponent and then put that result on the denominator. \displaystyle \int 3t-1 dt=\frac{3t^2}{2}-t+C. Then, plug in your initial values to find your C: \displaystyle \frac{3}{2}(1^2)-1+C=2. Then, \displaystyle C=\frac{3}{2}. Therefore, your answer is: \displaystyle x(t)=\frac{3}{2}t^2-t+\frac{3}{2}.

Example Question #151 : How To Find Position

Newton's Second Law of Motion tells us that a force exerted on an object will create an acceleration inversely proportional to the mass of the object being accelerated. This is expressed by the equation \displaystyle f=ma, where f is force, measured in Newtons, (1 N is the force required to accelerate 1 kilogram at 1 meter persecond per second), m is the mass of the object, measured in kilograms, and a is the acceleration, measured in meters per second per second.

A rocket-powered car is coasting at \displaystyle 25\,m/s when the driver starts up the engine again. The engine exerts a force of \displaystyle 30,000 \,N on the car, which weighs \displaystyle 1500\,kg. The driver shuts off the engine after 5 seconds. How far does the car travel in this time?

Possible Answers:

\displaystyle 125\,m

\displaystyle 250\,m

\displaystyle 625\,m

\displaystyle 375\,m

Correct answer:

\displaystyle 375\,m

Explanation:

We'll need to find the acceleration, and then work backwards to find the position. We can rewrite Newton's Second Law as \displaystyle a=\frac{f}{m}, which in this case gives us an acceleration of 

\displaystyle a(t)=\frac{30000 N}{1500 kg} = 20\,m/s^2.

The car's initial position and velocity are

\displaystyle \begin{align*} p_0&=0\,m \\ v_0 &= 25\,m/s\end{align*}

Initial and final time are given as 

\displaystyle \begin{align*} t_i &=0\,s \\ t_f &= 5\,s \end{align*}

Acceleration is the rate of change in velocity, which is the rate of change in position, so to find the equation for position, we'll ned to integrate and use initial conditions twice. 

\displaystyle \int a(t)dt=\int20 dt

To integrate, we use the following rule:

\displaystyle \int a\,dt = ax+C

Remember, when integrating we have to add the constant, C, to indicate that there's multiple functions that could be our answer.

Integrating then gives us:

\displaystyle \int a(t)dt=\int 20dt =20t+C

To solve for C, we'll use our initial condition, \displaystyle v(0)=25.

\displaystyle \\ v(0)=20(0)+C=25 \\ C=25 \\ v(t)=20t+25

We'll need to integrate again to find position:

\displaystyle \int v(t)=\int 20t+25 \, dt

using the following rule in addition to the earlier one:

\displaystyle \int x^n\,dx=\frac{x^{n+1}}{n+1}+C

Remember, when integrating we have to add the constant, C, to indicate that there's multiple functions that could be our answer.

Integrating then gives us:

\displaystyle \begin{align*} \int v(t)\,dt &= \int 20t+25\,dt \\ &=\frac{20t^2}{2}+25t+C \\ &=10t^2+25t+C \end{align*}

To solve for C, we'll use our initial condition, \displaystyle p(0)=0.

\displaystyle \\ p(0)=10(0^2)+25(0)+C=0 \\ C=0 \\ p(t)=10t^2+25t



which, evaluated at \displaystyle t=5, gives us

\displaystyle \begin{align*} p(4)&=10(5^2)+25(5) \\ &=10(25)+125 \\ &=375\,m\end{align*}

Example Question #152 : How To Find Position

A car starts at rest and accelerates in a straight line at \displaystyle 15\,m/s^2 for 20 seconds. How far does it travel?

Possible Answers:

\displaystyle 6,000\,m

\displaystyle 600\,m

\displaystyle 3,000\,m

\displaystyle 300\,m

Correct answer:

\displaystyle 3,000\,m

Explanation:

The equation for position is \displaystyle \frac{at^2}{2}, since we're starting from rest. Evaluating at \displaystyle t=20 gives us our answer, \displaystyle 3,000\,m

We'll need to work backwards from the acceleration to find the position. We're given the car's acceleration,

\displaystyle \begin{align*} a(t) &=15\,m/s^2\end{align*}

The car begins at rest, so 

\displaystyle \begin{align*} p_0&=0\,m \\ v_0 &= 0\,m/s\end{align*}

Initial and final time are given as 

\displaystyle \begin{align*} t_i &=0\,s \\ t_f &= 20\,s \end{align*}

Acceleration is the rate of change in velocity, which is the rate of change in position, so to find the equation for position, we'll ned to integrate and use initial conditions twice. 

\displaystyle \int a(t)dt=\int15 dt

To integrate, we use the following rule:

\displaystyle \int a\,dt = ax+C

Remember, when integrating we have to add the constant, C, to indicate that there's multiple functions that could be our answer.

Integrating then gives us:

\displaystyle \int a(t)dt=\int 15dt =15t+C

To solve for C, we'll use our initial condition, \displaystyle v(0)=0.

\displaystyle \\ v(0)=15(0)+C=0 \\ C=0 \\ v(t)=15t

We'll need to integrate again to find position:

\displaystyle \int v(t)=\int 15t \, dt

using the following rule:

\displaystyle \int x^n\,dx=\frac{x^{n+1}}{n+1}+C

Remember, when integrating we have to add the constant, C, to indicate that there's multiple functions that could be our answer.

Integrating then gives us:

\displaystyle \begin{align*} \int v(t)\,dt &= \int 15t\,dt \\ &=\frac{15t^2}{2}+C \\ &=7.5t^2+C \end{align*}

To solve for C, we'll use our initial condition, \displaystyle p(0)=0.

\displaystyle \\ p(0)=7.5(0^2)+C=0 \\ C=0 \\ p(t)=7.5t^2



which, evaluated at \displaystyle t=20, gives us

\displaystyle \begin{align*} p(4)&=7.5(20^2) \\ &=7.5(400) \\&=3000\,m\end{align*}

Example Question #153 : How To Find Position

The position of \displaystyle t= 1 is given by the following function: 

\displaystyle p(t)= (3x^2 + e^{2x})^2

Find the velocity.

Possible Answers:

\displaystyle 23.4

Answer not listed

\displaystyle 431.7

\displaystyle 126.8

\displaystyle 371.9

Correct answer:

\displaystyle 431.7

Explanation:

In order to find the velocity of a certain point, you first find the derivative of the position function to get the velocity function: \displaystyle p'(t)=v(t)

In this case, the position function is: \displaystyle p(t)= (3t^2 + e^{2t})^2

Then take the derivative of the position function to get the velocity function: \displaystyle v(t)= 2(3t^2 + e^{2t}) (6t+2e^{2t})

Then, plug \displaystyle t= 1 into the velocity function: \displaystyle v(1)= 2(3({\color{Blue} 1})^2 + e^{2({\color{Blue} 1})}) (6({\color{Blue}1 })+2e^{2({\color{Blue} 1})})

Therefore, the answer is: \displaystyle 431.7

 

Example Question #154 : How To Find Position

The position of \displaystyle t= 0 is given by the following function: 

\displaystyle p(t)= \sin(t^2+3t^4)

Find the velocity.

Possible Answers:

\displaystyle 1

\displaystyle 0

Answer not listed

\displaystyle 2

\displaystyle -1

Correct answer:

\displaystyle 0

Explanation:

In order to find the velocity of a certain point, you first find the derivative of the position function to get the velocity function: \displaystyle p'(t)=v(t)

In this case, the position function is: \displaystyle p(t)= \sin(t^2+3t^4)

Then take the derivative of the position function to get the velocity function: \displaystyle v(t)= \cos(t^2+3t^4) (2t+12t^3)

Then, plug \displaystyle t= 0 into the velocity function: \displaystyle v(t)= \cos({\color{Blue} 0}^2+3({\color{Blue} 0})^4) (2({\color{Blue} 0})+12({\color{Blue} 0})^3)

Therefore, the answer is: \displaystyle 0

 

Example Question #154 : How To Find Position

The position of \displaystyle t= 0 is given by the following function: 

\displaystyle p(t)= \sin(t^2+3t^4)

Find the velocity.

Possible Answers:

\displaystyle 1

\displaystyle 0

Answer not listed

\displaystyle 2

\displaystyle -1

Correct answer:

\displaystyle 0

Explanation:

In order to find the velocity of a certain point, you first find the derivative of the position function to get the velocity function: \displaystyle p'(t)=v(t)

In this case, the position function is: \displaystyle p(t)= \sin(t^2+3t^4)

Then take the derivative of the position function to get the velocity function: \displaystyle v(t)= \cos(t^2+3t^4) (2t+12t^3)

Then, plug \displaystyle t= 0 into the velocity function: \displaystyle v(t)= \cos({\color{Blue} 0}^2+3({\color{Blue} 0})^4) (2({\color{Blue} 0})+12({\color{Blue} 0})^3)

Therefore, the answer is: \displaystyle 0

 

Example Question #1011 : Spatial Calculus

A rocket is fired upwards from the Earth. It starts out sitting still on the launchpad, and its engines put out a force that would accelerate it upwards at \displaystyle 15\,m/s^2 in the absence of gravity. If the acceleration due to gravity is \displaystyle 9.8\,m/s^2, how far does the rocket travel in the first 4 seconds of its flight?

Possible Answers:

\displaystyle 120\,m

\displaystyle 240\,m

\displaystyle 41.6\,m

\displaystyle 396.8\,m

Correct answer:

\displaystyle 41.6\,m

Explanation:

We'll need to work backwards from the acceleration to find the position. We're given the rocket's acceleration, which is opposed by gravity, so the total acceleration will be

\displaystyle \begin{align*} a(t) &=15\,m/s^2-9.8\,m/s^2 \\ &=5.2\,m/s^2\end{align*}

The rocket begins at rest, so 

\displaystyle \begin{align*} p_0&=0\,m \\ v_0 &= 0\,m/s\end{align*}

Initial and final time are given as 

\displaystyle \begin{align*} t_i &=0\,s \\ t_f &= 4\,s \end{align*}

Acceleration is the rate of change in velocity, which is the rate of change in position, so to find the equation for position, we'll ned to integrate and use initial conditions twice. 

\displaystyle \int a(t)dt=\int5.2 dt

To integrate, we use the following rule:

\displaystyle \int a\,dt = ax+C

Remember, when integrating we have to add the constant, C, to indicate that there's multiple functions that could be our answer.

Integrating then gives us:

\displaystyle \int a(t)dt=\int 5.2dt =5.2t+C

To solve for C, we'll use out initial condition, \displaystyle v(0)=0.

\displaystyle \\ v(0)=5.2(0)+C=0 \\ C=0 \\ v(t)=5.2t

We'll need to integrate again to find position:

\displaystyle \int v(t)=\int 5.2t \, dt

using the following rule:

\displaystyle \int x^n\,dx=\frac{x^{n+1}}{n+1}+C

Remember, when integrating we have to add the constant, C, to indicate that there's multiple functions that could be our answer.

Integrating then gives us:

\displaystyle \begin{align*} \int v(t)\,dt &= \int 5.2t\,dt \\ &=\frac{5.2t^2}{2}+C \\ &=2.6t^2+C \end{align*}

To solve for C, we'll use out initial condition, \displaystyle p(0)=0.

\displaystyle \\ p(0)=2.6(0^2)+C=0 \\ C=0 \\ p(t)=2.6t^2



which, evaluated at \displaystyle t=4, gives us

\displaystyle \begin{align*} p(4)&=2.6(4^2) \\ &=2.6(16) \\&=41.6\,m\end{align*}

Example Question #151 : Position

If \displaystyle v(t)=2t-2 and \displaystyle x(1)=3, what is the position function?

Possible Answers:

\displaystyle x(t)=t^2-2t-4

\displaystyle x(t)=t^2+4

\displaystyle x(t)=t^2-2t+4

\displaystyle x(t)=-t^2-2t+4

\displaystyle x(t)=t^2-2t

Correct answer:

\displaystyle x(t)=t^2-2t+4

Explanation:

The first step in solving this problem is integrating the velocity function to get your position function. When integrating, remember to raise the exponent by 1 and then also put that result on the denominator: \displaystyle \int 2t-2dt=\frac{2t^2}{2}-2t=t^2-2t+C. Now, to figure out what C is, plug in your initial conditions given: \displaystyle (1^2)-2(1)+C=3; C=4. Plug in 4 for C to get your answer: \displaystyle x(t)=t^2-2t+4.

Example Question #151 : How To Find Position

What is the value of \displaystyle f{}'(1) if \displaystyle f(x)=3x^3-x^2+4x-1 ?

Possible Answers:

\displaystyle 1

\displaystyle 5

\displaystyle 0

\displaystyle 10

\displaystyle 11

Correct answer:

\displaystyle 11

Explanation:

First, you need to find the derivative of the function. When taling the derivative, multiply the exponent by the coefficient in front of the x term and then decrease the exponent by 1. Therefore: \displaystyle f{}'(x)=9x^2-2x+4. Now, plug in 1 for x to get your answer: 11.

Example Question #154 : How To Find Position

What is the position function if \displaystyle v(t)=4t-1 and \displaystyle x(1)=2?

Possible Answers:

\displaystyle x(t)=2x^2-x

\displaystyle x(t)=x^2-x+1

\displaystyle x(t)=2x^2-x-1

\displaystyle x(t)=2x^2-x+1

Correct answer:

\displaystyle x(t)=2x^2-x+1

Explanation:

To find the position function from the velocity function, you must integrate the velocity. When integrating, raise the exponent by 1 and then put that result on the denominator as well: \displaystyle \frac{4x^2}{2}-x+C=2x^2-x+C. Then, plug in your initial conditions to find C: \displaystyle 2(1^2)-1+C=2; C=1. Therefore, the position function is: \displaystyle x(t)=2x^2-x+1

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