Posted by **james** on Tuesday, November 23, 2010 at 9:03am.

A ferryboat traveling at a speed of 30 km/h attempts to cross a river with a current of 5 km/h. What is the boat's speed relative to the shore?

A.8 km/h

B.25 km/h

C.30.4 km/h

D.32.8 km/h

- Physics -
**drwls**, Tuesday, November 23, 2010 at 9:57am
It depends upon whether the ferry is travelling straight across (but aimed upstream) or aimed straight across (but drifting downsteam). The question does not make clear which it is.

In the first case, the answer is sqrt(30^2 -5^2) = 29.6 mph

In the secnd case, the answer is sqrt(30^2 + 5^2) = 30.4 mph

- Physics -
**Anonymous**, Monday, May 16, 2011 at 10:47am
32.8 km/h

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