9-5

$\displaystyle \left\langle K \right\rangle$	$\displaystyle = \frac{1}{T}\int_{0}^{T} dt\, K =\frac{\omega}{2\pi}\int_{0}^{2\pi/\omega} dt \, \frac{q^2 E_0^2}{4m \omega^2}\left[ 1-\cos(2\omega t)\right]$
	$\displaystyle =\frac{q^2 E_0^2}{8\pi m \omega } \left[ t -\frac{1}{2\omega } \s... ...c{2\pi}{\omega} - \frac{1}{2\omega} \left\{ \sin(4\pi)-\sin(0) \right\} \right]$
	$\displaystyle =\frac{q^2E_0^2}{4m\omega^2}$	(34)