Answer:
Part a)
![T=(1)/(9)\ sec](https://img.qammunity.org/2020/formulas/physics/middle-school/59ytkgl1zs5im840636hdr8htk7j5xxpvl.png)
Part b)
![v=45\ m/sec](https://img.qammunity.org/2020/formulas/physics/middle-school/9f4rojxvipjoh80vuj69q92092criackmm.png)
Step-by-step explanation:
Part a) What is the period of these waves?
we know that
Since wave frequency (f) is the number of waves per second, and the period (T) is essentially the number of seconds per wave, the relationship between frequency and period is
![f=(1)/(T)](https://img.qammunity.org/2020/formulas/physics/middle-school/70n1ge4t9yjxlmxiba3rirr9m8q57zz3ve.png)
![T=(1)/(f)](https://img.qammunity.org/2020/formulas/physics/high-school/c0tafhq7h957t0zih0dt8m9ps0g7o54pyg.png)
we have
![f=9\ Hz](https://img.qammunity.org/2020/formulas/physics/middle-school/bw8f51x395gzvt6qpygmwwj1c358wxv4dd.png)
Remember that
1 Hz is one cycle (or one wave) per second
so
![T=(1)/(9)\ sec](https://img.qammunity.org/2020/formulas/physics/middle-school/59ytkgl1zs5im840636hdr8htk7j5xxpvl.png)
Part b) What is the wave velocity?
we know that
The speed of a wave (v) is equal to the frequency multiplied by the wavelength
we have
![f=9\ Hz](https://img.qammunity.org/2020/formulas/physics/middle-school/bw8f51x395gzvt6qpygmwwj1c358wxv4dd.png)
![wavelength=5\ m](https://img.qammunity.org/2020/formulas/physics/middle-school/uq2gjl73o0epwi2g6wnbows51n9sbxfll7.png)
so
![v=(9)(5)=45\ m/sec](https://img.qammunity.org/2020/formulas/physics/middle-school/fb2scve0bxoojw6cm4e5qibkqiymppivna.png)