http://www.ck12.org Chapter 6. Transcendental Functions
- Polonium−210 is a radioactive isotope with half-life of 140 days. If a sample has a mass of 10 grams, how
much will remain after 10 weeks? - In the physics of acoustics, there is a relationship between the subjective sensation of loudness and the
physically measured intensity of sound. This relationship is called thesound levelβ.It is specified on a
logarithmic scale and measured with units ofdecibels(dB). The sound levelβof any sound is defined in
terms of its intensityI(in the SI-mks unit system, it is measured in watts per meter squared, W/m^2 ) as
β=10 log 10 I− 12.
For example, the average decibel level of a busy street traffic is 70 dB,normal conversation at a dinner table
is 55 dB, the sound of leaves rustling is 10 dB, the siren of a fire truck at 30 meters is 100 dB,and a loud rock
concert is 120 dB.The sound level 120 dB is considered the threshold of pain for the human ear and 0 dB is
the threshold of hearing (the minimum sound that can be heard by humans.)
a. If at a heavy metal rock concert adBmeter registered 130 dB,what is the intensityIof this sound level?
b. What is the sound level (indB) of a sound whose intensity is 2. 0 × 10 −^6 W/m^2?- Referring to problem #6, a single mosquito 10 meters away from a person makes a sound that is barely heard
by the person (threshold 0 dB). What will be the sound level of 1000 mosquitoes at the same distance? - Referring back to problem #6, a noisy machine at a factory produces a sound level of 90 dB.If an identical
machine is placed beside it, what is the combined sound level of the two machines?