Question

A girl can swim with speed 5 kmh still water. She crosses a river 2 km wide, where the river flows steadily u 2 kmh and she makes strokes to the river current. Find how far down the river she go when she reaches the other bank​

Answer 1

Answer:

800 m

Explanation:

Time taken to swim through = Distance / Speed

= 2/5 hours

So, distance she goes down the river by the flow of water = 2/5 × 2

= 4/5 km

= 800 m

Hope it helps.

Answer 2

Given: speed of girl swimming = 5km/h

          speed of river flowing = 2 km/h

          Distance of river = 2 km

To find Distance far from the point to another side of the bank.

Solution: Since two velocity moves at a right angle to each other. These two velocities being a vector quantity, will be added according to the rule of addition of vector.

The resultant velocity or the velocity of the girl will be

Resultant velocity = $\sqrt{v1^2 + v2^2 + 2v1v2Cos90$ ( As, cos90 = 0)

v' = $\sqrt{5^2 - 2^2$

v' = $\sqrt{25 - 4$

v' = $\sqrt{21$

Time is taken by the girl to reach the opposite side of the river = Distance/speed

2/ $\sqrt{21$ hour

So, the distance she goes down the river by the flow of water = 2/$\sqrt{21$ × 2

= 4/$\sqrt{21$km

So, the girl reaches 4/$\sqrt{21$km far down the river when she reaches the other bank.