Question

Each of two boats has a speed of 8 km/h. The speed of
river current is 6 km/h. Starting at the same instant,
the first boat crosses the river in least time, and the sec-
ond in least path. How must later the second boat
would arrive if the river is 2 km wide? ​

Answer 1

Answer:

Shortest possible path,s=1km

Time taken, t=15min=0.25hr

Speed in the direction of shortest path,

t

s

=

v

2

−u

2

Where, v=5kmh

−1

velocity of boat, u velocity of river.

t

s

=

v

2

−u

2

0.25

1

=

5

2

−u

2

u=3kmh

−1

Hence, velocity of river is 3kmh

−1

Explanation:

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