A man can swim with a speed of 4.0 km/h in still water. How long does

1.	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» 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.

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»

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.