[填空题]
When you slosh the waterlwwm h5p60-ru back and fcp9nwokp41 e -orth in a tub at just the right frequency, the water alternately rises and falls at each end, remaining relatively calm wecp-4pon1 k9 at the center. Suppose the frequency to produce such a standing wave in a 65-cm-wide tub is 0.85 Hz. What is the speed of the water wave? m/s