Given; number of oscillations = 40, time = 4 s
Time period can be calculated as follows:
Time taken for 40 oscillations = 4 second
Hence, time taken for 1 oscillation = 4 ÷ 40 = 0.1 second
Frequency can be calculated as follows:
Frequency = number of oscillations ÷ time
= 40 ÷ 4 = 10 Hz