Question

At a prayer meeting, the disciples sing JAI-RAM JAI-RAM. The sound amplified by a loudspeaker comes back after reflection from a building at a distance of$80m$ from the meeting. What maximum time interval can be kept between one JAI-RAM and the next JAI-RAM so that the echo does not disturb a listener sitting in the meeting. The speed of sound in air is $320m{s}^{-1}$.

Answer 1

Step 1. Given Data:

The distance of the building from the meeting is $80m$.

Total distance traveled by the sound after echo, $$\begin{gathered} S=80\times 2 \\ S=160m \end{gathered}$$

The speed of sound in air, $v_s=320m{s}^{-1}$.

Step 2. The maximum time interval, $t$ is:

Speed $=$Distance $/$ time

$$\begin{gathered} v_s=\frac{S}{t} \\ t=\frac{S}{v_s} \\ \Rightarrow t=\frac{160}{320} \\ \Rightarrow t=0.5sec \end{gathered}$$

Hence, the maximum time interval can be kept between one JAI-RAM and the next JAI-RAM so that the echo does not disturb a listener sitting in the meeting is $0.5sec$.