Question

A wave has a frequency of $120Hz$. Two points at a distance of $9m$ apart have a phase difference of ${180}^o$. The velocity of the wave is :

• A. $2340m/s$
• B. $2300m/s$
• C. $2330m/s$
• D. $2160m/s$

Answer 1

The correct option is D $2160m/s$

Phase difference between two points of wave is $\varphi ={180}^o=\pi$,

Time period of the wave is $T=\frac{1}{f}$ $=\frac{1}{120}$
Time taken by wave to travel distance between given two points is given by,

$t=\frac{\varphi }{2\pi }\times T$ $=\frac{\pi }{2\pi }\times \frac{1}{120}$$=4.16666\times {10}^{-3}$

$V=\frac{d}{t}$ $=\frac{9}{4.16666\times {10}^{-3}}$ .....($d=$ distance between two points)

$V=2160m/sec$