Is the derivative in my textbook correct here?

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SUMMARY

The discussion centers on the differentiation of kinetic and potential energy equations in a physics context. The user correctly identifies that the derivative of kinetic energy, represented as d/dx (T) = d/dx(1/2mx'²), results in mx'', while the potential energy derivative d/dx(U) = d/dx(1/2kx²) leads to kx', which is not equal to kx. The confusion arises from the need to differentiate with respect to time rather than position, as indicated by the notation x(t). The user acknowledges their oversight in applying the correct differentiation method.

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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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Here x is a function of t and the derivatives should be with respect to t. That's what x' implies.
 
(2.6) shows differentiation with respect to time. Your working is erroneously using differentiation with respect to x.
 
Oh right, it's x(t)... I guess the caffeine hasn't kicked in because that was really basic. Thank you!
 
No worries. Enjoy your coffee!
 
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.
 

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