Question

A motorboat can travel at 5 km/hr in still water. It travelled 90 km downstream in a river and then returned, taking altogether 100 hours. Find the rate of flow of the river.

Answer 1

Answer:

4 km/hr.

Step-by-step explanation:

Speed of boat in still water = x = 5 km/hr.

Let rate of flow of river = y km/hr. ∴ Speed of u/s = 5- y and speed of d / s = 5 + y

∴ 90/(5+y) + 90/(5-y) = 100 ⇒ y = 4 km/hr.

Answer 2

Answer:

Step-by-step explanation

Hi Dear,

● Answer -

vs = 3 km/h

● Explanation -

Let vm be velocity of motoorboat and vs be velocity of river stream.

Velocity of boat upstream -

vu = vm + vs

Velocity of boat downstream -

vd = vm - vs

Total distance travelled when boat returns to origin -

t = s/(vm+vs) + s/(vm-vs)

20 = 91/(10+vs) + 91/(10-vs)

Solving this eqn,

vs = 3 km/h

Therefore, rate of river flow is 3 km/h.

Hope this helps..you a lot