Question

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 1

Time taken to cross the river

=\(\frac {Width\,of\,the\, river}{Speed\, in\, this\,direction}\)

= \(\frac{1km}{4km^{-1}}\)

= \(\frac{1}{4} \,h = 15 \,min\)

Distance along the river covered in this time 

= Speed of the river x Time taken to cross the river

= 3 km h^-1 × 15 min = 0.75 km.