Question

A motor boat going downstream crosses a float at a point A. $60$ minutes later it turns back and after some time it again crosses the float, now the float is at a distance of $12$ km from the point A. The velocity of the stream is

• A. $8km/h$
• B. $4km/h$
• C. $6km/h$
• D. $10km/h$

Answer 1

Answer: (C)

$6km/h$

Let the velocity of boat $=V$
Velocity of stream $=v$
Float is at a point $A$
Boat coves $AB$ distance in $60min$
Float covers AC distance in $(t+60)min$
Boat covers BC distance in $tmin$
so, $v(60+t)=12$ ..... (1)
$(v+V)60=AB$ .... (2)
$(V-v)t=BC=AB-12$ ... (3)
Solving equation (1), (2) and (3) we get $t=60$
So, $v\left(120\right)=12$
$v=\frac{1}{10}km/min$$=\frac{60}{10}km/h=6km/h$