Answer:
[tex]v \approx 4.472\,\frac{ft}{s}[/tex], [tex]t = 10\,s[/tex]
Explanation:
Since man and river report constant speeds and velocities are mutually perpendicullar, the absolute speed of the man is calculated by the Pythagorean Theorem:
[tex]v = \sqrt{(4\,\frac{ft}{s} )^{2}+(2\,\frac{ft}{s} )^{2}}[/tex]
[tex]v \approx 4.472\,\frac{ft}{s}[/tex]
The required time to make the crossing is:
[tex]t = \frac{40\,ft}{4\,\frac{ft}{s} }[/tex]
[tex]t = 10\,s[/tex]
