A water wave is traveling down a narrow channel in a rundown district in Manhattan. A Styrofoam cup is floating on the surface of the water, tossed there by some careless passerby rushing to work. The city, in its rush, ignores this assault to civility, but you are waiting for a taxi, and you notice that it bobs from up to down to up in every two seconds. You decide to take a photograph in order to use up a roll of film. The data for the figure is taken from the photo.
What is the wavelength for this wave?