Chapter 26.2, Problem 22PP

To determine

The shortest time a reply can be expected.

Answer to Problem 22PP

The required time is $\boxed{t=1.25\times {10}^{-5}\text{s}}$ .

Explanation of Solution

Given:

Distance between earth and the moon is $d=376290\text{km}$ .

Formula used:

The expression for time is

  $t=\frac{d}{v}$…… (1)

Here, $d$ and $v$ are the distance and speed.

Calculation:

Substitute $376290\text{km}$ for $d$ and $3\times {10}^8{\text{ms}}^{\text{-1}}$ for $c$ in equation (1)

  $\begin{array}{l}t=\frac{376290\text{km}}{3\times {10}^8{\text{ms}}^{\text{-1}}}\\ t=\frac{376290\times {10}^3\text{m}}{3\times {10}^8{\text{ms}}^{\text{-1}}}\\ \boxed{t=1.25\times {10}^{-5}\text{s}}\end{array}$

Conclusion:

Hence,the required time is $\boxed{t=1.25\times {10}^{-5}\text{s}}$ .