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MCAT Question A Day - 9/14/13 - Answer!

A man drops a metal probe down a deep well-drilling shaft that is 3920 meters deep. If the temperature is 25°C, which is the closest estimate of how long it takes to hear the echo after the probe is dropped?

A.  5.0 s
B.  10 s
C.  20 s
D.  40 s

The correct answer is (D). There are two parts to the problem. First, you must find the length of time it takes the probe to fall to the bottom of the shaft, and then you need the amount of time it takes sound to travel back that same distance:

y = (1/2) gt2; therefore, t = (2y/g)(1/2)

t = (2.3920m / (9.8m/s2) )1/2

= (800s2)1/2