A swimmer can swim in still water at a speed

Question

of 9.31 m/s. He intends to swim directly
across a river that has a downstream current
of 4.35 m/s.
a) How many degrees from straight across
the river should he head? Let upstream be a
positive angle.
Answer in units of degrees
b) What is the magnitude of the swimmer’s
velocity relative to the bank?
Answer in units of m/s

Answer 1

(a)tanα =u/v=4.35/9.31=0.467.
α=arctan 0.467=25.04°
(b) v(rel) =sqrt(v²-u²)=sqrt(9.31²-4.35²)=8.23 m/s