Is the derivative in my textbook correct here?

In summary, the conversation discusses the differentiation with respect to time of the equations for kinetic and potential energy. The correct equation (2.3) is derived using the fact that potential energy relies on position and the derivative must be a velocity vector. The mistake in the working is due to using differentiation with respect to x instead of t. The error is corrected and the common factor is canceled, resulting in the correct equation. The conversation concludes with a reminder to enjoy coffee.
  • #1
whitejac
169
0

Homework Statement


Principle of Cons Ener.JPG


Homework Equations


d/dx

The Attempt at a Solution


d/dx (T) = d/dx(1/2mx'2) = mx''
d/dx(U) = d/dx(1/2kx2) = kx' ≠ kx

It's probably me who made an error because I know that that equation (2.3) is the one I should be getting, but I don't understand how they did it because potential energy relies on position, so the derivative has to be a velocity vector.
 
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  • #2
Here x is a function of t and the derivatives should be with respect to t. That's what x' implies.
 
  • #3
(2.6) shows differentiation with respect to time. Your working is erroneously using differentiation with respect to x.
 
  • #4
Oh right, it's x(t)... I guess the caffeine hasn't kicked in because that was really basic. Thank you!
 
  • #5
No worries. Enjoy your coffee!
 
  • #6
I think (2.3) starts out as ##m \ddot x \dot x + k x \dot x = 0## and the common factor ##\dot x## can be canceled from both sides.
 

Related to Is the derivative in my textbook correct here?

1. What is a derivative?

A derivative is a mathematical concept that represents the rate of change of a function. It is essentially the slope of a tangent line at a specific point on a curve.

2. How do I know if the derivative in my textbook is correct?

You can check the derivative in your textbook by using the rules and formulas for finding derivatives, such as the power rule, product rule, and chain rule. You can also use online calculators or software to verify the result.

3. What are some common errors that can occur when finding derivatives?

Some common errors when finding derivatives include forgetting to apply the chain rule, making arithmetic mistakes, and incorrectly differentiating exponential or logarithmic functions.

4. Can I use a different method to find the derivative?

Yes, there are various methods for finding derivatives, such as using the limit definition, implicit differentiation, and logarithmic differentiation. The method used may vary depending on the function and your personal preference.

5. How can I improve my understanding of derivatives?

To improve your understanding of derivatives, you can practice solving different types of derivative problems and review the rules and formulas. You can also seek help from a tutor or participate in online forums and discussions with other students and experts.

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