3. Two astronauts are 190 m apart in their spaceship. One speaks to the other. T

Question

3. Two astronauts are 190 m apart in their spaceship. One speaks to the other. The conversation is transmitted to earth via electromagnetic waves. The time it takes for sound waves to travel at 322 m/s through the air between the astronauts equals the time it takes for the electromagnetic waves to travel to the earth. How far away from the earth is the spaceship? 4. On a cloudless day, the sunlight that reaches the surface of the earth has an intensity of about 1.90 x 103 W/m2. What is the electromagneticenergy contained in 5.00 m2 of space just above the earth's surface?

Explanation / Answer

3.

constant : Speed of electromagnetic waves : 3×108 m/s

The time it takes for sound waves to travel at 322 m/s through air between the astronauts equals the time it takes for electromagnetic waves to travel to the earth.

Time taken for sound waves: t = d/v = 1.90 m÷ 322 m/s =0.0059 s

Time taken for electromagnetic waves: t = D/v = D/(3×108 m/s)

i.e. 0.0059 s = D/(3×108 m/s)

D = 1.77×106 m

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