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A man can swim with a speed of 4.0 km/h in still water. How long does he take to cross a river 1.0 km wide if the river flows steadily at 3.0 km/h and he makes his strokes normal to the river current ?

Q. 4.13  A man can swim with a speed of  4.0 \; km/h  in still water. How long does he take to cross a river 1.0 \; km/h  wide if the river flows steadily at 3.0 \; km/h  and he makes his strokes normal to the river current? How far down the river does he go when he reaches the other bank?

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The speed of man is (swim speed )  =    4 Km/h.

Time taken to cross the river will be : 

                                                                     =\ \frac{Distance}{Speed}

                                                                     =\ \frac{1}{4}\ =\ 15\ min.

Total distance covered due to the flow of the river:-  

                                                                        =\ Speed\ of\ river \times Time\ taken

                                                                         =\ 3\times\frac{1}{4}\ =\ 0.75\ Km

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