A ferry is trying to cross a 500 m wide river by starting from point A on one ba

Question

A ferry is trying to cross a 500 m wide river by starting from point A on one bank of the river with the following 4 possible destinations on the other bank of the river.

a. Point B, directly across from point A
b. Point C, which is 200 m upstream from point B
c. Point D, which is 200 m downstream from point B
d. Anywhere on the other bank but should take the minimum time to cross the river.

The boat is powered to travel 25 km/hr in still water and the river runs at 13 km/hr. Determine the time required to complete the crossing for a through d.

Explanation / Answer

For minimum time boat will travel perpendicular to the river side with velocity 25km/hr.

V = 25km/hr = 25 x 1000/3600 = 6.94m/s

hence it will take time =

500/6.94 = 72s = 1min 12s

The time required to complete the crossing for a through d is 72 seconds.

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