Question

A boat takes two hours to travel 8km down and 8km up the river when the water is still how much time will the boat take to make the same trip when the river starts flowing at 4km/hr

Answer 1

Given :
Boat can go 8km upstream in 1 hourAnd 8km downstream in 1 hour

Velocity of boat in still water=8km/hr

V1=Velocity of boat w.r.t to river=8km/hr

V2=velocity of riverw.r.t to ground=4km/hr

Down speed velcoity of boat=(8+4)km/hr=12km/hr

Upstream speed velocity of boat=(8-4)km/hr=4km/hr

Time taken downspeed=8/12

Time taken upstream=8/4
Total time= 8/12+8/4

=2/3+2
=2+6/3
=8/3
=2.66 sec

∴Time taken to by boat take to make the same trip when the river starts flowing at 4km/hr is 2.66sec

Answer 2

Answer:

Explanation:

Boat can go 8km upstream in 1 hour and 8km downstream in 1 hour

Velocity of boat in still water=8km/hr

Let V1=Velocity of boat w.r.t to river=8km/hr

and,

V2=velocity of river w.r.t to ground=4km/hr

Now , taking reference point as ground we have,

Down speed velcoity of boat=(8+4)km/hr=12km/hr

Upstream speed velocity of boat=(8-4)km/hr=4km/hr

Time taken downspeed=8/12

Time taken upstream=8/4

Total time= 8/12+8/4

=2/3+2

=8/3

=2.66 sec