The displacement / time graph shown represents a wave of wavelength 1.5 cm. What is the speed of the wave?

Answer:

Period = 2.0 s so frequency = (1 / 2.0) = 0.50 Hz
𝑣 = 𝑓 × 𝜆 = 0.50 × 1.5 = 0.75 cm / s
The answer is C