A transverse wave travelling through a medium has the waveform shown, where $y$ represents vertical displacement and $x$ represents horizontal distance. The wave moves at a speed of $20.0\ \text{cm s}^{-1}$. A particle in the medium vibrates vertically. Which graph of vertical displacement $y$ against time $t$ most closely shows the motion of this particle?
Physics 9702 · AS & A Level · Progressive waves