Because of barriers and obstructions you can see only a tiny fraction of a standing wave on a string. You do not know, for instance, how long the string is. All you know is that the speed of waves on the string is 100 m/s and that the distance ? in the sketch is 10 cm. All you know is that the speed of waves on the string is 100 m/s and that the distance ? in the sketch is 10 cm. Can you determine the frequency of the standing wave?

1. Sure, the frequency is 500 Hz.
2. No, you have no way to know the number
of nodes, for instance.
3. Sure, the frequency is 10 Hz.