A stone is dropped from the deck of the bridge. The sound of the splash reaches the deck 3 seconds later. If sound travels at 342 m/s in still air, how high is the deck of bridge above the water?

Answer 1

the falling time can be found by:

h-4.9t^2 = 0
t = √(h/4.9)

echo time is h/342, so

√(h/4.9) + h/342 = 3.0
h = 40.673 meters

Answer 2

Height of bridge can be calculated using 3rd kinematical equation i.e. S=ut+1/2at^2 put S=0 as displacement is 0 and a=-9.8 and u=0 as initial speed is 0 after calculating we will get the value of t=√(h/4.9) and then apply a simple formulae of speed=distance/time ,time we know speed of sound is given simply calculate the value of distance i.e.h=40.6728m