A boat moving at 9.5 km/hr relative to the water is crossing a river 3.9 km wide in which the current is flowing at 4.9 km/hr. At what angle upstream should the boat head to reach a point on the other shore directly opposite the starting point? (Assume 0 degrees is straight across)
go at 9.5 at angle A from straight across
0 = final upstream velocity = 9.5 sin A - 4.9
so sin A = 4.9/9.5