Calculus Quick Question: Differentiating Twice for Cosine Function Explanation

[Davio]

Homework Statement

y = A cos (kx-wt)

differentiate twice is -A^2k^2 cos (kx-wt)
Why?

Homework Equations

n/a

The Attempt at a Solution

-w^2 A cos (kx-wt)

 

[Hootenanny]

Apply the chain rule.

 

[arunbg]

Yes, you should use chain rule, but more importantly,what are you differentiating the function with respect to ? The answer the text gave has a quantity A^2, which I believe can't be obtained by differentiating the eqn, wrt any given variable in the function. Please check if you made an errors in copying the answer.

 

[Hootenanny]

Yes, you should use chain rule, but more importantly,what are you differentiating the function with respect to ? The answer the text gave has a quantity A^2, which I believe can't be obtained by differentiating the eqn, wrt any given variable in the function. Please check if you made an errors in copying the answer.

Good catch arunbg, didn't notice that myself

 

[arunbg]

Well, on second thought , you can get the answer if you derive the function with respect to x/A treating A as constant (using good old chain rule), but then that would be calculus, not physics

Oh, and hoot congrats for goin gold, and keep up the good work.

 

[Hootenanny]

Oh, and hoot congrats for goin gold, and keep up the good work.

Thanks arunbg , much appreciated. I've not 'seen' you much on the forums lately, hope everything is good at your end.