Question

A motor boat going down stream overcomes a float at a point A. 60 minutes later it turns and after some time passes the float at a distance of 12 km from the point A. The velocity of the stream is (assuming constant velocity for the boat in still water)

• A. $6km/h$
• B. $3km/h$
• C. $4km/h$
• D. $2km/h$

Answer 1

The correct option is A

$6km/h$

Let boat velocity w.r.t. water be 'v'

and water velocity in river be 'u'

then,~$AC=(v+u)1$ .......(1)

Assume time taken by boat to cover path C to B be 't'

then, $BC=(v-u)t$ ........(2)

and $AB=u(t+1)=12km$ ..............(3)

Now, AC = AB + BC

$\Rightarrow v+u=ut+u+vt-ut$

$\Rightarrow t=1hour$

and $u=6km/h$