Sound Intensity & Intensity Level



Consider all the sources of sound in the problems below to be point sources.



1)†††††††† A source of sound puts out 3.2( 10 - 7) J of energy in 0.15 seconds. Find the intensity 2.5 m away.




2)†††††††† You measure an 85 dB shriek from a screaming child 1.5 m away. If the shriek lasts 4.5 seconds, how much energy did the child convert into sound?




3)†††††††† What is the intensity of a 118 dB sound?




4)†††††††† If the intensity level at 3.0 m was 118 dB, what was the intensity level at 25 m?




5)†††††††† A 45 dB sound wave strikes an eardrum whose area is 5.0(10 - 5) m2. How long would it take the eardrum, in seconds, to receive 1.0 J of energy?




6)†††††††† A candy bar contains 275,000 calories of chemical potential energy. If all of that energy were converted to sound in 2.0 seconds, how many dB would you measure 15 m away? One calorie equals 4.186 Joules.




7)†††††††† A 1200 kg car is moving at 25 m/s. It locks up its brakes and slides to a stop. If all of its kinetic energy were converted to sound in 3.5 seconds (which is totally unrealistic, but letís pretend) what would be the intensity level of the sound 5.0 m away?




8)†††††††† Imagine youíre standing near an airplane with four equally noisy engines. You measure a 120 dB sound intensity. If the pilot shut down three of the four engines, how many dB would you measure? (Itís not 30 dB.)




9)†††††††† The person to your right is yelling at 85.0 dB (as measured by you, not him) and the person to your left is yelling at 95.0 dB. How many dB will you measure if both are yelling at the same time? (Itís definitely not 180 dB.)