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CBSE Class 9 Answered

a construction worker's helmet slips and falls when he is 78.4m above the ground he hears the sound of a helmet hitting the ground 4.23 seconds after it slipped find the speed of sound in air
Asked by Shagun Rastogi | 01 Jan, 2014, 11:53: AM
answered-by-expert Expert Answer

Given,

h = 78.4 m

g = 9.8 m/s2

u = 0

Time taken to hear the sound, T = 4.23 sec

v 2 = u 2 + 2 gh

     = 0 + 2 gh

v2 =√2gh

v= √2 x 9.8 x 78.4

v= 39.2

This is the speed of the helmet.

Now using,

v = u + gt

39.2 = 0 + 9.8 x t

39.2/9.8 = t

t= 4 sec

Therefore time taken by helmet to reach the ground is 4 sec.

T – t = 4.23 – 4 =0.23 s

In this time sound travels the height 78.4 m (distance)

So, speed of sound in air = distance/time

=78.4/0.23

=340.86m/s

Answered by Faiza Lambe | 01 Jan, 2014, 07:07: PM

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