Question

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.

Answer 1

Answer:

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