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theuniverse

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## Homework Statement

A particle undergoes simple harmonic motion in both the x and y directions simultaneously. Its x and y coordinates are given by

x=asin(wt)

y=bcos(wt)

a. Eliminate t from these equations to show that the path of the particle in the x-y plane is an ellipse.

b. Calculate the kinetic and potential energy at a point on the particle’s trajectory. Show that the ellipse is a path of constant total energy, and show that the total energy is given by the sum of the separate energies of the x and y oscillations.

## Homework Equations

Equation of an ellipse: (x/a)^2+(y/b)^2=1

KE = 1/2=mv^2

PE = ??

## The Attempt at a Solution

a) I rearranged the parametric eqns. like so: x/a=sinwt and y/b=coswt, squared both sides and using trig identities eliminated the term (sin^2wt+cos^2wt) leaving 1 on the right side and therefore getting the equation of an ellipse: (x/a)^2+(y/b)^2=1

b)This is where I'm having some troubles... I am pretty sure that I can calculate the KE of the particle by looking at:

KE(x)= 1/2*mv(t)^2

= (1/2)mw^2(acoswt)^2

KE(y)= -(1/2)mw^2(bsinwt)^2

but I don't know how to come up with the equations for the potential energy.

Regrading the fact that the ellipse is a path of constant total energy, I am thinking of showing that when the particle is on the x-axis it means that y=0 thus eliminating the y component of the energy, same goes for when its on the y axis. which essentially can be modeled with a cosine function where energy is always constant but changes from component to component.

I'd appreciate any help or some input on my attempt at the solution.

Thanks!