While talking to a friend, a construction worker momentarily set her cell phone down on one end of an iron rail of length 7.50 m. At that moment, a second worker dropped a wrench so that it hit the other end of the rail. The person on the phone detected two pulses of sound, one that traveled through the air and a longitudinal wave that traveled through the rail. (Assume the speed of sound in iron is 5,950 m/s and the speed of sound in air is 343 m/s). A) Which pulse reaches the cell phone first?
B) Find the separation in time (in s) between the arrivals of the two pulses.

A)

The impulse that reaches the cell phone first is the Longitudinal wave

B)  0.0206  seconds

Explanation:

length of Iron rail = 7.5 m

speed of sound in Iron = 5950 m/s

speed of sound in Air = 343 m/s

A) Determine which pulse reaches the cell phone first

The impulse that reaches the cell phone first is the Longitudinal wave

 Time for longitudinal pulse to be detected =  7.5 / 5950 = 0.00126 s

  Time for pulse through air to be detected = 7.5 / 343 = 0.02186  s

B) separation in time between the arrivals of the two pulses

   ΔT = 0.02186 - 0.00126  = 0.0206  seconds

the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.