A river flows with a speed of 3km/h in still water. A man who can swim with a speed of 5km/h wishes to reach a point on the other bank just opposite to the starting point. In which direction should he put his strokes and how long will he take to cross the river of width 1.2km? Please try to provide a diagram and step by step explanation.

Certain bacteria (such as aquaspirillum magnetotacticum) tend to swim toward the earth’s geographic north pole because they contain tiny particles, called magnetosomes, that are sensitive to a magnetic field. if a transmission line carrying 100 a is laid underwater, at what range of distances would the magnetic field from this line be great enough to interfere with the migration of these bacteria? (assume that a field less than 5% of the earth’s field would have little effect on the bacteria. take the earth’s field to be 5.0 * 10-5 t, and ignore the effects of the seawater.)