# Equation of motion, functions

A simple harmonic oscillator, of mass m and natural frequency w_0, experiences an oscillating driving force f(t)=m a cos(wt). Therefore, its equation of motion is

d^2x/dt^2 + w^2_0x = acos(wt)

where x is the position. Given that at t=0 we have x=dx/dt=0, find the function x(t). Use BOTH with variation of the parameters and guessing methods. Describe the solution if w is approximately, but not exactly, equal to w_0. Give an example of a physical system where this happens.

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The equation is:

(1.1)

The general solution is given by:

(1.2)

Where is the solution of the associated homogenous equation

(1.3)

and is a particular solution to equation (1.1).

This equation is a second order linear equation with constant coefficients.

To solve equation (1.3) we "guess" a solution in the form:

(1.4)

Plugging it in the homogenous solution we get:

(1.5)

Where

Thus the two homogenous solutions are:

(1.6)

Since we are interested in real solutions, and the homogenous solution is a linear combination of these two linearly solutions, we can use Euler's identity

(1.7)

To express the two ...

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The expert examines equation of motion and functions.