A student wants to swim across a river of 100 m, the current is 1 m/s. He wants to swim the fast as possible. Another wants to swim the fast as possible and avoid a waterfall at the end of the river ( 10 to the end of the river). If they both use 2 m/s speeds when swimming, how fast do they go? And for the one avoiding a waterfall at what angle should he aim at?? I don't understand this, thanks in advance....