A surfer is riding a wave with an amplitude of 20 feet and a period of 40 feet. If the wave completes a period in 10 seconds, what is the speed of the surfer? Select one: a. 400 feet per second b. 40 feet per second c. 4 feet per second d. 1414 feet per second Solution Amplitude = 20 feet Period = 40 feet The wave completes a period in 10 seconds. Speed of the surfer =Distance/Time =Period length /Time = 40 /10 = 4 feet per second Option C.