Chapter 16, Problem 72A

To determine

The reason that it takes $5\text{s}$ to hear thunder when lightning is $1.6\text{km}$ away.

Answer to Problem 72A

Since the speed of sound is less than the speed of light, thus the lightning can be seen almost instantly while it is heard after $5\text{}\text{s}$ .

Explanation of Solution

Introduction:

  $\text{Distance}=\text{Speed}\times \text{Time}$

The speed of sound is known as, $v=343\text{}\text{m/s}$

Now, if the lightning is $1.6\text{km}$ away, then the time taken by sound to reach us will be,

  $\begin{array}{c}\text{Time = }\frac{\text{Distance}}{\text{Speed}}\\ =\frac{\text{1}\text{.6}\times {\text{10}}^3\text{m}}{\text{343}\text{m/s}}\\ \approx 5\text{}\text{s}\end{array}$

Conclusion:

The speed of light is very large due to which thunder can be seen almost instantly while its sound is heard after $5\text{}\text{s}$