### Q.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 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?

**Answer:-**

Speed of the man, *v*_{m} = 4 km/h

Width of the river = 1 km

Time taken to cross the river = Width of the river / Speed of the river

= 1/4 h = 1 × 60 / 4 = 15 min

Speed of the river, *v*_{r} = 3 km/h

Distance covered with flow of the river = *v*_{r} × *t*

*= 3 *×* *1 / 4* = *3 / 4 km

= 3 × 1000 / 4

= 750 m