Initial State: An 8-month old child is at rest at the bottom of a staircase. Final State: The 8-month old child is at rest at the top of the staircase. Notes: The system includes the child and earth. The child uses the steps to slowly crawl up the staircase

Option (a) is the correct answer.

Explanation:

Using the Pythagoras theorem, we will calculate the the distance of and as follows.

                   = 24.17

                   = 22.56

Therefore, the path difference will be as follows.

                      = 24.17 - 22.56

                      = 1.61 m

Formula for constructive interference is as follows.

                      = 1.61 m      (for n = 1)  

Therefore, frequency will be calculated as follows.

                            =

                            = 213.043 Hz

Thus, we can conclude that frequency produced by the speakers to create perfectly constructive interference is 213.04 Hz.