Ahelicopter is hovering at an altitude of 200m above the surface of the lake. a speaker on the helicopter is sending out sound waves which are reflected from both the surface of the water and bottom of the lake. if the differences in arrival times of the two echoes is measured to be 0.24s, what is the depth of the lake? (the atmospheric temperature is 20°c)

Explanation:

The first echo travels from the helicopter to the surface and back.  The second echo travels from the helicopter to the surface to the bottom of the lake and then back.

We know the difference in time is 0.24 s, so the time it takes the sound wave to travel through only the water is 0.24 s.  Since the sound wave covers the distance twice (first from the surface to the bottom, then the bottom to the surface), we only want half the time, 0.12 s.

The speed of sound in water at 20°C is 1481 m/s.  Therefore:

d = 1481 m/s × 0.12 s

d = 178 m

The depth of the lake is 178 meters (round as needed).

-first use of geothermal energy occurred more than 10,000 years ago in north america by american paleo-indians

-the first industrial use of geothermal energy began near pisa, italy in late 18th century

-in 1904, italian scientist piero ginori conti invented the first geothermal electric power plant in which steam was used to generate the power

-with the above experiment, the first geothermal plant in usa started in 1922 with a capacity of 250 kilowatts

-however, in 1946 first ground-source geothermal heat pump installed at commonwealth building in portland, oregon

-during the 1960’s, pacific gas and electric began operation of first large scale geothermal power plant in san francisco, producing 11 megawatts

-in 1973, when oil crisis began many countries began looking for renewable energy sources and by 1980’s geothermal heat pumps (ghp) started gaining popularity in order to reduce heating and cooling costs

-as effect of climate change started showing results, governments of various countries joined hands to fight against it, for which kyoto protocol was signed in japan in 1997, laid out emission targets for rich countries and required that they transfer funds and technology to developing countries, 184 countries have ratified it

hope this

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