As a jet aircraft exceeds the speed of sound the jet sets up a shock wave that may be heard as a sonic boom if the shock wave occurs close to Earth. the speed of sound varies with the temperature. The following formula is the speed in km/h, based on the temperature of the gas in degrees Kelvin and the molecular mass of the gas in grams per mole: S=389T/m

a. If the average molar mass of a normal air mixture is 28.8 g/mol, what is the speed of sound at an altitude of 4.9 km where the temperature is 256 K(-17C)?

b. What is the speed of sound in helium if the temperature is 300 K (27C). The molar mass of helium is 4.0 g/mol. This is related to why you voice sounds so funny when you breathe helium from a balloon.

c. Rearrange the formula to isolate the temperature, and then calculate the temperature at which the speed of sound in a normal air mixture is 1000 km/h. Assume the average molar mass of the air molecules is 28.8 g/mol.