Question

when a stone is dropped into a lake from a the top of a tower 400ft high,the impact will be heard after how many seconds?

Answer 1

Answer:

Time taken to reach stone to lake

$s = ut + \frac{1}{2} g {t}^{2} \\ u = 0 \: \: and \: \: g = 32.2 \: \: \frac {ft}{ {s}^{2} } \\ 400 = \frac{1}{2} \times 32.2 \times {t}^{2} \\ t = \sqrt{400 \times 16.1} \approx \: 80 \: secs$

Now speed of sound is almost 1125 ft/s , so sound will take 400/1125 = 0.35 seconds to travel back

So total time ( approx ) = 80.35 seconds