Question

Find the phase velocity of the wave whose $y-x$ graph is shown at two instants.

• A. $10\text{m/s}$
• B. $15\text{m/s}$
• C. $25\text{m/s}$
• D. $20\text{m/s}$

Answer 1

The correct option is C $25\text{m/s}$

From figure, we can deduce that, the wave is travelling in the positive $x-$ direction .
From the two graphs, phase difference between points $A$ and $B$ is given by
$\Delta x-v\Delta t=0$
From the data given in the diagram,
$\Delta x=50\text{m}$ and $\Delta t=2s$
$\therefore$ Phase velocity, $v=\frac{\Delta x}{\Delta t}$
$\Rightarrow v=\frac{50}{2}=25\text{m/s}$
Thus, option (c) is the correct answer.