A boat, which has a speed of 9.00 m/s in still water, would like to reach a point on the shore directly across a river. The river has a current of 3.50 m/s and the river is 550 meters wide.

Question

A boat, which has a speed of 9.00 m/s in still water, would like to reach a point on the shore directly across a river. The river has a current of 3.50 m/s and the river is 550 meters wide. 
a. In what direction should the boat be aimed in order for the boat to head directly across
the river?
b. How long will it take the boat to reach the opposite shore?

oobleck · Answer

It has to travel upstream at an angle θ (where straight across is θ=0) such that sinθ = 3.50/9.00 the distance traveled will be 550/cosθ and of course, time = distance/speed, so ...

henry2, · Answer

a. Vr = Vb - 3.5i = 9.0 = resultant Velocity, Vb = 9 + 3.5i = 9.66m/s[21.25o] CCW. Direction = 21.25o CCW = 21.25o N. of E. b. d = V * t = 550, 9*t = 550, t = 61 s.