The speed of a motor boat in still water is 20 km/hr and river flow is 5 km/hr. A float is droped from the boat when it starts moving upstream. After moving 1.5 km the boat returns back. The boat will catch the float after(from initial instant).
(A) 6 min
(B) 12 min
(C) 10 min
(D) 15 min
Correct option (B) 12 min
Explanation:
speed of boat in upstream = 15 km/hr
Distance = 1.5 km
time t1 = 1.5/15 = 6 min
Dist. moved by float in this time
speed of boat w.r.t. float = 20 km/hr,
t2 = 2 km/20 = 6 min.
