Answer Part A and B and show all work. Part A) Bob hears music from a speaker th

Question

Answer Part A and B and show all work.

Part A)   Bob hears music from a speaker that is radiating sound waves uniformly in all directions. The initial distance from Bob to speaker is d. If Bob moves to a new distance of 3d, what will be the percentage change in the intensity of the waves that reach him

Part B)   Suppose the area of Bob’s eardrum is 1 x 10-4 square meters. If a sound wave with intensity 2 x 10-5 W/m2 reaches Bob’s eardrum, how many Joules of energy would be absorbed by the eardrum in 15 minutes?

Explanation / Answer

PART A)

Let old intensity at distance d be I

Let new intensity at distance 3d be I new

Intensity falls off a 1/r^2

I /Inew = 9

percentage change intensity is ( I -I NEW)/I = 8/9 = 88 .8 PERCENT

PART B)

Energy = Intensity*Area*Time

Energy = 2 x 10-5 W/m2*1 x 10-4m2 *15*60 sec

Energy = 0.18 * 10-5 J

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