Given

• \[ \begin{align*} 1.\quad f &= \text{2 waves in 5 s} \\ &= \frac{2}{5} \text{ per second} \\ &= 0.4 \text{ wave per second} \\ &= 0.4/\text{s} \\ &= 0.4\ \text{Hz} \end{align*} \]
• \[ \begin{align*} 2.\quad & \text{From point A to point B is 1 m.} \\ & \text{Between these points are two waves,} \\ & \text{therefore, the length of each wave is 0.5 m.} \end{align*} \]

Given: λ = 0.5 m

Asked:

1. a. velocity (v)
2. b. period (T)

Solution

• \[ \begin{align*} \text{a.} \quad v &= \lambda f = (0.5\,\text{m})(0.4/\text{s}) \\ v &= 0.2\,\text{m/s} \end{align*} \]
• \[ \begin{align*} \text{b.} \quad T &= \frac{\lambda}{v} = \frac{0.5\,\text{m}}{0.2\,\text{m/s}} \quad \text{(cancel the meter units)} \\ T &= 2.5\,\text{s} \end{align*} \]