A boat, whose speed in still water is 8.0 m/s, crosses a river with a current of 6.0 m/s. If the boat heads perpendicular to the current, what is the speed of the boat relative to an observer standing
On the shore as it crosses the river?
A) 10.0 m/s
B) 5.3 m/s
C) 6.0 m/s
D) 8.0 m/s

Question

Quizplus · Accepted Answer

The speed of the boat relative to an observer on the shore is the resultant of the boat's speed in still water and the current's speed. This can be found using the Pythagorean theorem since the boat's direction and the current's direction are perpendicular to each other. $ \sqrt{(8.0)^2 + (6.0)^2} = \sqrt{64 + 36} = \sqrt{100} = 10.0 $ m/s.

A Boat, Whose Speed in Still Water Is 8