Chapter 9, Problem 5MPS

To determine

To Find: The speed of the wind.

Answer to Problem 5MPS

  $60mph$

Explanation of Solution

Given: An airplane travels $1800km$ in $6h$ flying with the wind. It travels only two third as far in the same time against the wind.

Let $x$ be the speed of wind

Speed of the plane is $300mph$

Then

Speed against the wind $300-x$

Speed with the wind is $300+x$

Now

Distance against the wind is $1200mi$

Distance with wind is $1800mi$

We know that

  $\text{time=}\frac{\text{distance}}{\text{rate}}$

Then

  $\frac{1200}{300-x}=\frac{1800}{300+x}$

Solving for speed of wind

  $\begin{array}{l}360000+1200x=540000-1800x\\ 3000x=180000\\ x=60mph\end{array}$

Hence, the speed of the wind is $60mph$