Question

A 0.20-km wide river has a uniform flow speed of 4.054 m/s toward the east. A boat with a speed of 80 m/s relative to the water leaves the south bank and heads in such a way that it crosses to a point directly north of its departure point. How long does it take the boat to cross the river? 29s 23s 25s 27s 17s

Answer 1

To counter the river's drift velocity, the boat will have a component of velocity of the magnitude of 4.054m/s to the west. The velocity component from South to North can be calculated using vector addition formula

$v_{SN} = \sqrt{8^2 - 4.054^2} = 6.89m/s$

Therefore the time is given by

$t = \frac{d}{v_{SN}} = \frac{200}{6.89} = 29m/s$

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