The correct option is B 6.53 s
Given,
Initial velocity, u=0 m/s
Depth D = 180 m
Acceleration due to gravity, g=10 ms−2
Speed of sound. vsound=340 ms−1
T1 = time taken by the stone to reach depth D when it is thrown
T2 = time taken by sound to reach the surface
From second equation of motion, we have,
s=ut+12at2
D=12×10×T21
T1 = √2×D10 = √D5 =√1805 = 6 s
Time taken for the sound to travel from bottom of the well to the surface
We know, time=distancespeed
⇒ T2 = 180340 = 0.53 s
Total time, T1+T2 = 6.53 s