Chapter 26, Problem 48A

Susie hammers on a block of wood when she is 85 m from a large brick wall. Each time she hits the block, she hears an echo 0.5 s later. With this information, show that the speed of sound is 340 m/s.

To determine

To show the speed of sound is 340 ${\mathrm{ms}}^{-1}$ when Susie hammers on a block of wood when she is 85 m from a large brick wall and hears an echo 0.5 s later.

Answer to Problem 48A

The speed of sound is 340 ${\mathrm{ms}}^{-1}$ when Susie hammers on a block of wood when she is 85 m from a large brick wall and hears an echo 0.5 s later.

Explanation of Solution

Given:

Distance of the large brick wall from Susie ( $\mathrm{d}$ ) = 85 m

Time taken by sound wave (echo) to travel to the wall and reflect back to Susie = 0.5 s

So,

Time taken by sound wave to travel to the wall ( $\mathrm{t}$ ) only = $\frac{0.5s}{2}=0.25s$

Formula used:

  $\mathrm{Speed}ofsoundwave(s)=\frac{Distance(d)ofthewall}{time(t)}$

Calculation:

Putting the values and we get;

  $\mathrm{Speed}ofsoundwave(s)=\frac{85m}{0.25s}=340m{s}^{-1}$

  $\mathrm{Speed}ofsoundwave(s)=340m{s}^{-1}$

Conclusion:

Thus, the speed of sound is 340 ${\mathrm{ms}}^{-1}$ when Susie hammers on a block of wood when she is 85 m from a large brick wall and hears an echo 0.5 s later.