Please answer this soon people.?

Question

A boy finds an abandoned mine shaft in the woods, and wants to know how deep the hole is. He drops in a stone, and counts 4 seconds before he hears the "plunk" of the stone hitting the bottom of the shaft. Approximately how deep is the shaft? (Assume a gravitational acceleration of 9.8 m/s2 and no significant air resistance.)

Your choices are:

# A. 14 meters

# B. 24 meters

# C. 39 meters

# D. 78 meters

Answer 1

D.  You use the formula s =1/2 at^2 where a is acceleration (9.8) and t time (4 sec.).

Actually the depth will be less due to the time taken for the sound to travel up and the resistance of the air on the falling stone.

Answer 2

Distance = Do + Vot + 1/2at^2

Distance is unkown

Do=0

Vo=0

a=9.8 m/s^2

t = 4

Distance = 1/2 * 9.8 * 4^2

Dist = 8 * 9.8

Dist = 78.4 m

so 78 m

Answer 3

Distance = S in metres = ?

initial velocity = U in metres/sec = 0

Time = T in secs = 4

Acceleration = A = m/s^2 = 9.81

General formula S = UT + 1/2AT^2

S = (0 x 4) + (0.5 x 9.81 x 4 x 4)

S = 0 + 78.48

Depth is approx 78 meters