Answer: The observing friend will the swimmer moving at a speed of 0.25 m/s.
Explanation:
Hence the resultant velocity is given as, [tex]S_{R}[/tex] = S — S 0[tex]S_{0}[/tex]
[tex]S_{R}[/tex] = 1.25 — 1
[tex]S_{R}[/tex] = 0.25 m/s.
Therefore, the observing friend will see the swimmer moving at a speed of 0.25 m/s due to resistance produced by the current of the river.