Chapter 6.4, Problem 3P

a.

To determine

To find: Rowing speed in still water and speed of the current

Answer to Problem 3P

Rowing speed in still water (a) is 7/2 miles per hour

Speed of the current (b) is 3/2 miles per hour

Explanation of Solution

Given:

Row Upstream speed is 2 mi/h

Row Downstream speed is 5 mi/h

Concept Used:

Row Upstream speed means the speed of object and the current (or water flow) is in opposite direction as they are in opposite direction that means their speed will subtract

Row Downstream speed means the speed of object and the current (or water flow) is in same direction as they are in same direction that means their speed will add

Calculation:

Let the rowing speed of object in still water is a

And the speed of current (or water flow) is b

a>b (always true for the numeric questions)

Then, for Upstream:

  $a-b=2$

For downstream:

  $a+b=5$

On adding both the equations:

  $\begin{array}{l}2a=7\\ \boxed{a=\frac{7}{2}mi/h}\end{array}$

Put in equation $a-b=2$

  $\begin{array}{l}\frac{7}{2}-b=2\\ b=\frac{7}{2}-2\\ \boxed{b=\frac{3}{2}mi/h}\end{array}$

b.

To determine

To explain: The outcome of trying to row upstream

Answer to Problem 3P

We can’t row upstream in these conditions

Explanation of Solution

Given:

Rowing speed in still water (a) is 3 mi/h

Speed of current (b) is 4 mi/h

For upstream:

  $a-b=3-4=-1mi/h$

Hence, we can’t row upstream in these conditions