Question

A man can swim at 4 ft/s in still water. He wishes to cross tje 40-ft wide river to point B, 30 ft downstream. If the river flows with a velocity of 2 ft/s, determine the speed of the man and the time needed to make the crossing. Note While in the water he must not direct himself toward point B to reach the point.

Answer 1

`v \approx 4.472\,(ft)/(s)`,
`t = 10\,s`

Step-by-step 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:

`v = \sqrt{(4\,(ft)/(s) )^(2)+(2\,(ft)/(s) )^(2)}`

`v \approx 4.472\,(ft)/(s)`

The required time to make the crossing is:

`t = (40\,ft)/(4\,(ft)/(s) )`

`t = 10\,s`