Jack and Jill blow their whistles at the same time producing sound waves at frequencies of 400 Hz and 404 Hz respectively. How many beats per second are heard from the superposition of the two waves?

Choose one answer.
a. 400
b. 404
c. 4
d. 8

Beats = 404 - 400 = 4.

To determine the number of beats per second heard from the superposition of the two waves, we need to find the difference in frequency between the two waves. The number of beats per second is equal to this frequency difference.

In this case, the frequency of Jack's whistle is 400 Hz and the frequency of Jill's whistle is 404 Hz. The difference in frequency is 404 Hz - 400 Hz = 4 Hz.

Therefore, the correct answer is c. 4.