X = Acos(ωt) + Bsin(ωt) derivation

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In summary, the conversation discusses how to derive the equation x = Acos(ωt) + Bsin(ωt) from the formula F = -mω2x and how it is used in physics contests. The conversation also touches on Hooke's law and SHM for a spring, and explains the general solution to the differential equation mx''=-mω2x. The final conclusion is that the relation between Acos(ωt) + Bsin(ωt) and Asin(ωt) is given by A\cos(ωt) + B\sin(ωt) = \sqrt{A^2+B^2}\sin(ωt+θ_0).
  • #1
sparkle123
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How do you derive x = Acos(ωt) + Bsin(ωt) from F = -mω2x and what is the former used for?

Thank you!
 
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  • #2
Hey sparkle!

If this is homework, you should show some effort before we're allowed to help you (PF regulations I'm afraid).
What's it for?
 
  • #3
This was on a list of things you should know for physics contests. :)
 
  • #4
Well, what can you make of it?
 
  • #5
Well, F = -mω2x is hooke's law
and SHM for a spring is like x = Asin(ωt)
 
  • #6
So what's your question?

Actually, F=ma and "a" is the second derivative of "x" with respect to time.
So you have mx''=-mω2x.
The general solution to this differential equation is x = Acos(ωt) + Bsin(ωt).
 
  • #7
so would you get from Acos(ωt) + Bsin(ωt) to Asin(ωt)?
thanks!
 
  • #8
sparkle123 said:
so would you get from Acos(ωt) + Bsin(ωt) to Asin(ωt)?
thanks!

The relation is:
$$A\cos(ωt) + B\sin(ωt) = \sqrt{A^2+B^2}\sin(ωt+θ_0)$$
 
  • #9
thank you! :)
 

FAQ: X = Acos(ωt) + Bsin(ωt) derivation

1. How do you derive the equation X = Acos(ωt) + Bsin(ωt)?

The equation X = Acos(ωt) + Bsin(ωt) can be derived using the trigonometric identity cos(ωt + θ) = cos(ωt)cos(θ) - sin(ωt)sin(θ). By setting θ = arctan(B/A), we can rewrite the equation as X = (Acos(ωt) + Bsin(ωt))cos(arctan(B/A)) - (Bcos(ωt) - Asin(ωt))sin(arctan(B/A)). Simplifying this expression gives us X = A(cos(ωt)cos(arctan(B/A)) - sin(ωt)sin(arctan(B/A))) + B(sin(ωt)cos(arctan(B/A)) + cos(ωt)sin(arctan(B/A))). Using the trigonometric identities cos(arctan(B/A)) = A/√(A^2 + B^2) and sin(arctan(B/A)) = B/√(A^2 + B^2), we get the final form of X = Acos(ωt) + Bsin(ωt).

2. What is the meaning of the constants A and B in the equation X = Acos(ωt) + Bsin(ωt)?

In the equation X = Acos(ωt) + Bsin(ωt), A and B are the amplitudes of the cosine and sine functions, respectively. They determine the maximum displacement of the wave from its equilibrium position. The value of A and B also affect the shape and size of the wave.

3. How is the angular frequency ω related to the period of the wave in the equation X = Acos(ωt) + Bsin(ωt)?

The angular frequency ω is related to the period of the wave by the equation T = 2π/ω, where T is the period and ω is the angular frequency. This means that as the value of ω increases, the period of the wave decreases and vice versa.

4. Can the equation X = Acos(ωt) + Bsin(ωt) be used to describe all types of waves?

Yes, the equation X = Acos(ωt) + Bsin(ωt) can be used to describe all types of waves, including mechanical, electromagnetic, and sound waves. However, the values of A and B may vary depending on the specific type of wave.

5. Is there a specific range of values for the constants A and B in the equation X = Acos(ωt) + Bsin(ωt)?

There is no specific range of values for A and B in the equation X = Acos(ωt) + Bsin(ωt). However, their values must be greater than or equal to 0, as they represent the amplitudes of the wave. Additionally, the values of A and B can be any real numbers, positive or negative, and can also be equal to 0.

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