Question

A person stands between two vertical cliffs 400m from the nearer cliff. The cliffs are x distance apart. Every time the person strikes the rock once, two echoes are heard, the first one after 2.5s and the second one 2.0 s later. Calculate

1. the speed of the sound in air 
2. the value of x

Answer 1

1. s = 2d
          t
   = 2 x 400
        2.5
   = 320ms⁻¹
2. 2(x − 400) = (2.5 +2)s  
   x = 1120m 

Answer 2

320m/s                                                1120

Answer 3

320m/s.                                               1120

Answer 4

320m/s.                                              1120