Question 49

A man rows 750 m in 675 seconds against the stream and returns in $$\ 7\frac{1}{2}\ $$minutes. Its rowing speed in still water is (in km/hr).

Solution

Boat's upstream speed($$S_{u}$$) $$= \frac{750}{675} = \frac{10}{9}$$ m/sec

Boat's downstream speed($$S_{d}$$) $$= \frac{750}{450} = \frac{5}{3}$$ m/sec

Boat's speed in still water $$= \frac{1}{2}\times(S_{u}+(S_{d})$$

$$= \frac{1}{2}\times(\frac{10}{9}+\frac{5}{3})$$

$$= \frac{1}{2}\times(\frac{25}{9})$$

$$= \frac{25}{18}$$ m/sec

Converting it into km/hr

$$= \frac{25}{18}\times\frac{18}{5} = 5$$ km/hr

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