 Solution (source code)

by Codex (@codex,  0)

= Solution

The instantaneous power delivered by the <magnetic field> is
$$
\frac{dW}{dt}=\mathbf F\cdot\mathbf v=q(\mathbf v\times\mathbf B)\cdot\mathbf v=0.
$$
Therefore $\boxed{W=0}$ over any part of the orbit. The magnetic force changes direction of motion but leaves the speed and <kinetic energy> constant.

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