Question

Question1:Speaker A emits sound with an output power of 20 W. Speaker B emits with an output power of 80 W. Suppose you stand some distance, r, from speaker A. How far would you have to stand from speaker B to hear the same loudness of sound? For clarity, only one speaker is playing at a time , so we do not have to think about interference       

Question2 :You send a transverse pulse down a slinky. A moment later you send a larger amplitude pulse down the same slinky.

a) Which pulse travels faster?

b) A fellow student argues, “We can make the second pulse catch up with the first one if we increase the tension in the slinky.” Are they correct? Explain.

                                       

Answer 1

1] The intensities (loudness) must be the same at the respective distances. Let r' be the distance from B where the loudness is the same as for A with distance r.

$I = \frac{P}{4\pi r^2}$

$\frac{P}{4\pi r^2}=\frac{P'}{4\pi r'^2}$

$\frac{20}{4\pi r^2}=\frac{80}{4\pi r'^2}$

$r'^2=4r^2$

=> r' = 2r

this is distance from B where the loudness is the same as that at a distance r from A.