Answer :
We are told that 4.0 complete waves pass a fixed point in 10 seconds. Using these data, we can find the frequency of the wave, which is given by the number of complete cycles per second:
[tex] f=\frac{N}{t}=\frac{4}{10 s}=0.4 Hz [/tex]
Now we can find the period of the wave, which is the reciprocal of the frequency:
[tex] T=\frac{1}{f}=\frac{1}{0.4 s}=2.5 Hz [/tex]
So, the correct answer is (3) 2.5 s.
