College Physics (4th Edition)

The maximum speed of vibration is $2.5\times 10^{-6}~m/s$
We can find the angular frequency $\omega$: $\omega = 2\pi~f = (2\pi)(4000~Hz) = 8000\pi~rad/s$ We can find the maximum speed: $v_m = A~\omega$ $v_m = (0.10\times 10^{-9}~m)~(8000\pi~rad/s)$ $v_m = 2.5\times 10^{-6}~m/s$ The maximum speed of vibration is $2.5\times 10^{-6}~m/s$.