If the average sound intensity inside the dorm cafeteria is 1.59 times 10^-5 W/m

Question

If the average sound intensity inside the dorm cafeteria is 1.59 times 10^-5 W/m^2, determine the amount of energy going into each ear (area = 2.40 times 10^-3 m^2) during a 3-hour meal. J After your school's team wins the regional championship, students go to the dorm roof and start setting off fireworks rockets. The rockets explode high in the air and the sound travels out uniformly in all directions. If the sound intensity is 1.77 times 10^-6 W/m^2 at a distance of 255 m from the explosion, at what distance from the explosion is the sound intensity half this value? m A stereo speaker is placed between two observers who are 35 m apart, along the line connecting them. If one observer records an intensity level of 58 dB, and the other records an intensity level of 85 dB, how far is the speaker from each observer? closer observer m farther observer m

Explanation / Answer

1.

Iavg = average intensity = 1.59 x 10-5 W/m2

A = area = 2.40 x 10-3 m2

t = time = 3 h = 3 x 60 x 60 sec

amount of energy is given as

E = Iavg A t

E = (1.59 x 10-5) (2.40 x 10-3) (3 x 60 x 60)

E = 0.000412 J

Q-2

I1 = 1.77 x 10-6

I2 = I1/2 = (1.77 x 10-6)/2 = 8.85 x 10-7

r1 = 255 m

r2 = ?

using the formula

I1/I2 = r22/r12

(1.77 x 10-6)/(8.85 x 10-7) = (r2/255)2

r2 = 360.62 m

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