Question

In: Physics

A stone is dropped from the top of a cliff. The splash it makes when striking...

A stone is dropped from the top of a cliff. The splash it makes when striking the water below is heard 2.5 s later. The speed of sound in air is 343 m/s. How high is the cliff?

Solutions

Expert Solution

Solution:

Let t1 be the time taken by the rock to touch the water and.

t2 be the time taken by the sound to reach us.

Given that t1 + t2 = 2.5 s    -------------(1)

Velocity of sound v = 343 m/s

Let S be the distance taveled by the rock.
          t2 = S/v = S/343 ........... (2)
from eq. of motion, S = (1/2)g(t1)2    (initial speed u =0)
         t2 = [(1/2)(9.8 m/s2)(t1)2]/(343 m/s) = 0.014286(t1)2 ..........(3)
substitute the eq (3) in eq (1), we get
     0.014286(t1)2 + t1 - 2.5 = 0
On solving the above quadratic equation we get
                      t1 = 2.416 s

Hence distance covered by the rock is

                      S = (1/2)(9.8 m/s2)(2.416 s)2

   S = 28.63 m


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