Question

A stone is dropped into a well with water 80 m below the ground level. If the speed of the sound in air is 320 m/s, what time after dropping the stone will the splash be heard? (g = 10 ms2)

Answer 1

Answer:

see total time taken will be the sum of time taken(t1) by stone to cover 80m + time taken (t2)by sound of splash to come up 80m

T=t1+t2

for finding time taken by stone to fall from 80m

we use s=ut+1/2gt1² (taking u =0)

80=0+1/2*10*t1²

80=5t1²

t1=4sec (neglecting -ve value)

now calculating t2(time taken by sound to reach up)

t2= 80/320

t2=0.25sec

therefore total time taken=t1+t2

4+0.25=4.25 sec...

hope it helps..