Answer:
The law of inertia
Explanation:
A body at rest will remain at rest, and a body in motion will remain in motion unless it is acted upon by an external force
If the current takes him downstream we must find the resultant vector of the velocities:

Then if the river is 3000 m-wide the swimmer will have to pass:
1.3520747 · 300 = 4056.14 m t = 4056.14 m : 1 m/s
a ) It takes
4056.15 seconds ( 1 hour 7 minutes and 36 seconds ) to cross the river.
b ) 0.91 · 3000 =
2730 mHe will be 2730 m downstream.
Point a because point a is the highest at potential energy converting into the highest kinetic energy.