Question

A man wishes to cross a rive in a boat. If he crosses
the river in minimum time, then he takes 10 min
with a drift of 120 m. If he crosses the river taking
shortest route, he takes 12.5 min, find the velocity
of the boat with respect to water.​

Answer 1

refer to the above picture

all the best for your future friend

buboi......

Answer 2

Answer:

Explanation:

Width = d

Man = V

River = v

In minimum time, he goes perpendicular to the river.

d/V = 10 min------(1)

v x 10 min = 120 m, so v = 12 m /min

In minimum distance, the resultant of the velocities is perpendicular to river

If he is at angle x with the perpendicular

V sinx = v = 12-----(2)

V cosx = d / 12.5-----(3)

Squaring and adding (2) and (3)

2V^2 = 144 + d^2 / 156.25 -----(4)

Putting value of V from (1) in (4),

d^2 /50 = 144 + d^2 /156.25

d^2 = 10500 m

d = 100m

There could be some calculation error, but the method is correct.

Explanation: