Chapter 8.7, Problem 40PPS

To determine

To calculation:

The speed of the current.

Answer to Problem 40PPS

The speed of current is about $2.3$ ft/sec.

Explanation of Solution

Given information:

Stream at a speed = $3.3$ feet per second

Stream $=80$ feet wide

Jonas crosses the stream $=20$ seconds

Calculation:

Jonas crosses the stream in $20$ seconds and the river is $80$ feet wide therefore, the velocity is $80/20$ or $4ft/\sec$ , which is the current resultant of Jonas speed and speed of the stream.

Now use the Pythagorean theorem to get the value of $x$ , the speed of the stream.

  $\begin{array}{l}{x}^2+{3.3}^2=4^2\\ x^2+10.89=16\\ x^2=5.11\\ x=\sqrt{5.11}\approx 2.3\end{array}$

Hence, the current speed is about $2.3$ ft/sec.