Question1

A 25MW Jet engine produces a sound level of 120dB, threshold of pain at a distance of 100m from the engine Recall the threshold of human hearing is 1 * 10^(-12)W/m^2

a)What portion of jet power is lost to producing this sound?

b) You are at your silent summer house (40dB) and you can just hear the sound of the smae jet engine at the airport. How far away is your house from the airport?

c) Is result of your simple calculation reasonable?

Question2

Powdered steel is placed in a container filled with oxygen and fitted with a piston that moves to keep the pressure in a container constant at one atmosphere. A chemical reaction occurs that produces heat. To keep contents at a constant temperature of 28.7^oC, it is needed to remove 5.51083 × 10^5J of heat from container as it contracts. During the chemical reaction, it is found that 1.8 mol of oxygen is consumed. Find the internal energy change for the system of iron and oxygen. The universal gas constant is 8.31451 J/K mol.