Q: A swimmer moving upstream passes a float at point P. After two hour, he returns and at this instant it meets the float again at a distance 15 km from the point P. If the swimmer velocity in water remains constant, then find the speed of river flow.
(a) 5 kmh-1
(b) 10 kmh-1
(c) 3.75 kmh-1
(d) 7.5 kmh-1
Ans: (d)
Solution:Let Speed of river flow is v
$\displaystyle v = \frac{distance}{time}$
$\displaystyle v = \frac{15}{2}$
v = 7.5 km/h
As swimmer velocity in water remains constant, the speed of river flow is 7.5 km/h