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f (frequency) = V / y   where V is the speed of sound and y the wavelength

f = 1500 m/s / 1.5 m = 1000 / sec

T (period) = 1 / f = .001 sec

Suppose you replace the horn by a drum then the period would be the time between the beats of the drum - now if the source is moving towards the observer then the distance between crests  of the wave produced by the drum will be shortened by V * T because of the motion of the drum "towards" the observer, and since the wavelength is shorter the frequency heard by the observer will be higher, and the higher the speed of of the car the shorter the wavelength as seen by the observer and the higher the frequency.

Also, if the car is moving away from the observer then the distance between the crests of the wave emitted will be further apart, and the observer will hear a lower frequency.

so here is the information for current research:

-nrel's geothermal analysts, scientists, and engineers perform a full range of research from developing advanced methods of locating and accessing geothermal resources to exploring innovative technologies to extract and produce clean energy from the heat of the earth

and here is the information for the technology of geothermal energy:

-it's clean and sustainable

-resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the earth's surface, and down even deeper to the extremely high temperatures of molten rock called magma

-almost everywhere, the shallow ground or upper 10 feet of the earth's surface maintains a nearly constant temperature between 50° and 60°f (10° and 16°c)

-geothermal heat pumps can tap into this resource to heat and cool buildings

-a geothermal heat pump system consists of a heat pump, an air delivery system (ductwork), and a heat exchanger-a system of pipes buried in the shallow ground near the building

-in the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system

-in the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger

-the heat removed from the indoor air during the summer can also be used to provide a free source of hot water

c. newton's third law of motion