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embphysics
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Homework Statement
(a) Consider a system with one degree of freedom and Hamiltonian [itex]H = H (q,p)[/itex] and a new pair of coordinates Q and P defined so that [itex]q = \sqrt{2P} \sin Q[/itex] and [itex]p = \sqrt{2P} \cos Q[/itex]. Prove that if [itex]\frac{\partial H}{\partial q} = - \dot{p}[/itex] and [itex]\frac{\partial H}{\partial p} = \dot{q}[/itex], it automatically follows that [itex]\frac{\partial H}{\partial Q} = - \dot{P}[/itex] and [itex]\frac{\partial H}{\partial P} = \dot{Q}[/itex]. In other words, the Hamiltonian formalism applies just as well to the new coordinates a to the old. (b) Show that the Hamiltonian of a one-dimensional harmonic oscillator with mass m = 1 and force constant k=1 is [itex]H = \frac{1}{2}(q^2 + p^2)[/itex].(c) Show that if you rewrite this Hamiltonian in terms of Q and P defined in the two equations above, then Q is ignorable. What is P?(d) Solve the Hamiltonian equation for Q(t) and verify that, when rewritten for q, your solution gives the expected behavior.
Homework Equations
The Attempt at a Solution
All right, here is the solution I have written so far:
The system under consideration is constrained to move in such a way that its position can be adequately described by a single coordinate. In this case, the coordinate is q. However, there is another single coordinate that sufficiently describes the system's position, too, and that would be Q. The coordinate transformation between Q and q is [itex]q = \sqrt{2P} \sin Q[/itex]. Given a position coordinate Q describing the system's position relative to some origin, we can find the corresponding coordinate q that describes the same location.
Here is where I am having trouble, writing the Hamiltonian as a function of q and p:
[itex]H(q,p) = \dot{q}p - L(q, \dot{q})[/itex]