Using Calculus to Solve for Time in a Particle's Position Function

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In Summary, when solving for a function's derivative, you need to use the definition of the derivative, expand your (t + h)3 and (t + h)2 terms and then combine all like terms in the numerator. You then take the limit as h --> 0 and you will be left with your derivative.
  • #1
morphine
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0

Homework Statement



(Sorry I don't know how to insert nice looking equations)

If the position function of a particle is given by
s = t3 - 4.5t2 - 7t, t >= 0
, the particle reaches an instantaneous
velocity of 5 m/sec when t =
1
2
3
4
5


Homework Equations




The Attempt at a Solution


Well, the problem I'm having is how to do this to find t instead of finding the velocity. If I attempt to find the derivative, I always get stuck at something like:

lim h -> t [(t+h)3 - 4.5(t+h)2 - 7(t+h)] - [t3 - 4.5t2 - 7t] ALL OVER h

I can play with that a little bit, but it never gets anywhere. thanks
 
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  • #2
Assuming that you have to use the definition of the derivative, expand your (t + h)3 and (t + h)2 terms and then combine all like terms in the numerator. There should be some simplification so that you can then divide by the h in the denominator. Finally, take the limit as h --> 0 and you will be left with your derivative.
 
  • #3
Well you need to find the derivative. I can tell you the answer is 4 but you should find it for yourself. If that is where you get stuck, expand it out and cancel out like terms. What i mean by that is calculate (t+h)(t+h)(t+h) and then find 4.5(t+h)(t+h) and so on. You will see that all terms without the h cancel out, and you are able to divide everything by h.

Keep in mind that the answer you will then have is now a speed function, not a position function. If you are still stuck post again.
 
  • #4
OK, I did that, and assuming my algebra was right I got 3t2 - 9t - 7

And here I'm stuck again. Do I just set that equal to 5 and solve?
 
  • #5
That is the correct value of s'(t). Now evaluate s'(t) at t = 1, 2, 3, 4, and 5.
 
  • #6
Awesome now I see. Thanks for the help Mark and dacruick.

Ill probably have a few more questions over the next few hours.
 

FAQ: Using Calculus to Solve for Time in a Particle's Position Function

What is Calculus I?

Calculus I is a branch of mathematics that deals with the study of change and motion. It involves the use of mathematical concepts and techniques such as limits, derivatives, and integrals to solve problems related to rates of change and optimization.

What are the main topics covered in Calculus I?

The main topics covered in Calculus I include limits, derivatives, and integrals. Limits are used to determine the behavior of a function as the input variable approaches a certain value. Derivatives are used to calculate the rate of change of a function at a specific point. Integrals are used to calculate the area under a curve or the accumulation of a quantity.

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Calculus I has numerous real-life applications, including physics, engineering, economics, and statistics. For example, it is used to calculate the velocity and acceleration of objects in motion, optimize the design of structures, and model the behavior of markets.

How can I prepare for a Calculus I exam?

To prepare for a Calculus I exam, it is important to review the main concepts and practice solving problems. You can also seek help from a tutor or join a study group to clarify any doubts and discuss challenging problems. Make sure to also get enough rest and eat well before the exam.

Is Calculus I difficult to learn?

The difficulty of learning Calculus I can vary depending on the individual. Some people may find it challenging, while others may find it easier. However, with proper dedication, practice, and support, anyone can learn and understand the concepts of Calculus I.

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