Michelle is enjoying a picnic across the valley from a cliff. She is playing mus

Question

Michelle is enjoying a picnic across the valley from a cliff. She is playing music on her radio (assume it to be an isotropic source) and notices an echo from the cliff. She claps her hands and the echo takes 2.3 s to return.

Michelle is enjoying a picnic across the valley from a cliff. She is playing music on her radio (assume it to be an isotropic source) and notices an echo from the cliff. She claps her hands and the echo takes 2.3 s to return. Given that the speed of sound in air is 343 m/s on that day, how far away is the cliff? If the intensity of the music 1.0 m from the radio is 1.0 10-5 W/m2, what is the intensity of the music arriving at the cliff?

Explanation / Answer

a. velocity = distance/time

here distance = 2S since the sound is reflecting form surface

so

2S = 343* 2.3 = 789 mts

s = 394.5 m

b. Intensity I = power/area = p/4pi r^2

I2/I1 = r1^2/r2^2

I2 = 1*10^-5 *1^2/394.5^2

I2 = 6.42 *10^-11 W/m^2

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