Calculus 1 : How to find velocity

Study concepts, example questions & explanations for Calculus 1

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Example Questions

Example Question #121 : Calculus

Find \displaystyle f'(x) at \displaystyle x=0 for

\displaystyle f(x)=e^{2x^2+4x}.

Possible Answers:

\displaystyle 0

\displaystyle 4

\displaystyle 1

\displaystyle 2

Correct answer:

\displaystyle 4

Explanation:

First we need to find \displaystyle f'(x) before evaluating it at \displaystyle x=0.

\displaystyle f(x)=e^{2x^2+4x}

\displaystyle f'(x)=(4x+4)e^{2x^2+4x}.

This was found by using the definition of the derivative for exponential functions.

The definition is,

\displaystyle f(x)=e^{g(x)}

\displaystyle f'(x)=g'(x)e^{g(x)}.

 

Now we can evaluate \displaystyle f'(x) at \displaystyle x=0

\displaystyle f'(0)=(4\cdot0+4)e^{2\cdot (0)^2+4\cdot 0}

\displaystyle f'(0)=4\cdot e^{0}=4

 

Example Question #121 : Spatial Calculus

At time \displaystyle t=0, a diver jumps from a cliff that is \displaystyle 72 feet above the water. The cliff diver's position is represented by the following: \displaystyle s(t)=-36t^2+36t+72, where \displaystyle s is measured in feet and \displaystyle t is measured in seconds.

What is the velocity of the cliff diver when he/she hits the ground?

Possible Answers:

\displaystyle -36f/s

\displaystyle -72f/s

\displaystyle -108 f/s

\displaystyle -144 f/s

Correct answer:

\displaystyle -108 f/s

Explanation:

First, set \displaystyle s(t) to equal \displaystyle 0

\displaystyle 0=-36(t^2-t-2)=-36(t-2)(t+1).

Then solve for \displaystyle t:

\displaystyle t-2=0 and \displaystyle t+1=0.

Therefore, \displaystyle t=-1, 2. Since \displaystyle t represents time in seconds, we can rule out \displaystyle t=-1.

This means that it takes the cliff diver 2 seconds to reach the water. Next, take the derivative of \displaystyle s(t) by using the Power Rule \displaystyle x^n=nx^{n-1} and plug in for \displaystyle t\displaystyle \\s'(t)=-72t+36\\ s'(2)=-72(2)+36=-108.

The cliff diver's velocity was \displaystyle -108 f/s when he/she hit the water.

Example Question #121 : Velocity

Mark throws a tennis ball into the air at \displaystyle t=0. It's position is represented by \displaystyle s(t)=-4t^2+2t-8, where \displaystyle t is in seconds and \displaystyle s is in meters.

What is the velocity of the ball at \displaystyle t=2?

Possible Answers:

\displaystyle 16m/s

\displaystyle 18m/s

\displaystyle 2m/s

\displaystyle -14m/s

Correct answer:

\displaystyle -14m/s

Explanation:

First, take the first derivative of the equation by using the Power Rule \displaystyle x^n=nx^{n-1} : 

\displaystyle s'(t)=-8t+2.

Then, plug in for \displaystyle t=2

\displaystyle \\s'(2)=-8(2)+2\\ s'(2)=-16+2=-14.

Therefore, the velocity is \displaystyle -14m/s.

Example Question #121 : Velocity

Sara goes to a skate park and enters a bowl. The bowl at the park is represented by \displaystyle s(t)=10t^2-16t-2, where \displaystyle s represents distance in feet and \displaystyle t represents time in seconds. 

What is Sara's velocity at \displaystyle t=3?

Possible Answers:

\displaystyle 44ft/s

\displaystyle 60ft/s

\displaystyle 16ft/s

\displaystyle 20ft/s

Correct answer:

\displaystyle 44ft/s

Explanation:

Take the first derivative of the equation by using the Power Rule \displaystyle x^n=nx^{n-1} : 

\displaystyle s'(t)=2(10)t-16=20t-16.

Then, plug in \displaystyle t=3

\displaystyle 20(3)-16=44.

Therefore, the velocity at \displaystyle t=3 is \displaystyle 44ft/s.

Example Question #122 : Calculus

A cannonball is shot from a cannon. Its position is represented by \displaystyle s(t)=-5t^2-3t+15, where \displaystyle s represents distance in meters and \displaystyle t represents time in seconds.

What is the velocity of the cannonball at \displaystyle t=1?

Possible Answers:

\displaystyle -31m/s

\displaystyle -3m/s

\displaystyle -13m/s

\displaystyle -10m/s

Correct answer:

\displaystyle -13m/s

Explanation:

Take the first derivative by using the Power Rule \displaystyle x^n=nx^{n-1} of \displaystyle s(t),

\displaystyle s'(t)=-5(2)t-3=-10t-3.

Then, plug in \displaystyle t=1,

\displaystyle s'(1)=-10(1)-3=-13.

Example Question #121 : Velocity

Leela throws a football across a field. It's position is represeted by \displaystyle s(t)=-6t^2+8t-12, where \displaystyle s represents distance in feet and \displaystyle t represents time in secomds.

What is the velocity at \displaystyle t=4?

Possible Answers:

\displaystyle -40ft/s

\displaystyle -4ft/s

\displaystyle 4ft/s

\displaystyle -12ft/s

Correct answer:

\displaystyle -40ft/s

Explanation:

Take the first derivative by using the Power Rule \displaystyle x^n=nx^{n-1} of \displaystyle s(t),

\displaystyle s'(t)=-6(2)t+8=-12t+8.

Then, plug in for \displaystyle t=4,

\displaystyle \\s'(4)=v(4)\\v(4)=-12(4)+8=-48+8\\ v(4)=-40.

Example Question #127 : Calculus

Lucas tosses an orange into the air. Its position is represented by \displaystyle s(t)=-2t^2+6t-4, where \displaystyle s represents distance in feet and \displaystyle t represents time in seconds. 

What is the velocity of the orange at \displaystyle t=3?

Possible Answers:

\displaystyle -18ft/s

\displaystyle -12ft/s

\displaystyle 6ft/s

\displaystyle -6ft/s

Correct answer:

\displaystyle -6ft/s

Explanation:

Take the first derivative by using the Power Rule \displaystyle x^n=nx^{n-1} of \displaystyle s(t),

\displaystyle s'(t)=-2(2)t+6=-4t+6.

Then, plug in \displaystyle t=3

\displaystyle -4(3)+6=-12+6=-6.

Example Question #121 : Calculus

A ball is dropped into a bowl. The position of the ball is represented by \displaystyle s(t)=8t^2-6t+4, where \displaystyle s represents distance in inches and \displaystyle t represents time in seconds.

What is the velocity of the ball at \displaystyle t=2?

Possible Answers:

\displaystyle 26in/s

\displaystyle 32in/s

\displaystyle 16in/s

\displaystyle -6in/s

Correct answer:

\displaystyle 26in/s

Explanation:

Take the first derivative by using the Power Rule \displaystyle x^n=nx^{n-1} of \displaystyle s(t),

\displaystyle s'(t)=8(2)t-6=16t-6.

Then, plug in for \displaystyle t=2,

\displaystyle \\s'(2)=v(2)\\ v(2)=16(2)-6\\v(2)=32-6=26.

Example Question #121 : Calculus

A given arrow has a position defined by the equation \displaystyle p(t)=12t^{2}+5(t)-10. What is its velocity at time \displaystyle t=2?

Possible Answers:

\displaystyle 49

\displaystyle 53

\displaystyle 55

\displaystyle 43

\displaystyle 60

Correct answer:

\displaystyle 53

Explanation:

By definition, velocity is the first derivative of position, or \displaystyle v(t)=p'(t).

Given a position 

\displaystyle p(t)=12t^{2}+5(t)-10, we can use the power rule 

\displaystyle \frac{d}{dt}t^{n}=nt^{n-1} where \displaystyle n\neq0 to determine that 

\displaystyle v(t)=p'(t)=24t+5.

Therefore, at \displaystyle t=2

\displaystyle v(2)=p'(2)=24(2)+5=48+5=53.

Example Question #121 : Spatial Calculus

Aaron's car has a position defined by the equation \displaystyle p(t)=15t^{2}+17t-9. What is its velocity at time \displaystyle t=2?

Possible Answers:

\displaystyle 79

\displaystyle 81

\displaystyle 80

\displaystyle 77

\displaystyle 78

Correct answer:

\displaystyle 77

Explanation:

By definition, velocity is the first derivative of position, or \displaystyle v(t)=p'(t).

Given a position 

\displaystyle p(t)=15t^{2}+17t-9, we can use the power rule 

\displaystyle \frac{d}{dt}t^{n}=nt^{n-1} where \displaystyle n\neq0 to determine that 

\displaystyle v(t)=p'(t)=30t+17.

Therefore, at \displaystyle t=2

\displaystyle v(2)=p'(2)=30(2)+17=60+17=77.

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