# Physics

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As measured from centre ice, a single wildly cheering hockey fan can produce a sound intensity level of 60dB. What sound intensity level would be produced by
20 000 cheering fans?

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If sound waves travel through the ground with an average speed of 6150 m/s and a powerful explosion occurs 5.00kn away, how much time will elapse between when you feel the vibration from the explosion and hear the explosion? Use v=344m/s for the speed of sound in air.

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You pick up two metal rods that look the same and appear to have the same mass. However, when you strike the first rod, it produces a sound that has a much higher frequency than the second rod. What does this result tell you about the speed of sound in the two rods?

THANKS.

• Physics - ,

1. L = Lₒ + 10•logN = 60 +10•log(20000) =60 +10•4.3 =103 db.
2. t1 = s/v1 = 5000/6150 =0.81 s.
t2 = s/v2 = 5000/344=14.53s.
Δt =14.53 – 0.81 =13.72 s.
3. The frequency is set by the oscillating body which sets up the sound waves. The speed of the waves is determined by the elastic/inertial properties of medium and the wavelength.
λ = v/f (the higher wavelength the higher frequency)
The speed of sound doesn’t depend on frequency.

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