1, Humankind consumes energy at a rate of about 2 kilowatts (kW) per capita, whe

Question

1, Humankind consumes energy at a rate of about 2 kilowatts (kW) per capita, where 1 watt (W) is 1 joule/second (J/s), with the joule being the SI unit of energy. The world population at the beginning of 2015 was about 7.22 billion people, use this value in your calculations.
Estimate the world's total yearly energy consumption.

2. Space explorers land on a planet whose radius is5.30 % smaller than Earth's but whose mass is14.0 % greater than Earth's.
Find the acceleration of gravity at this planet's surface.

3. The gravitational force between two identical lead spheres of mass 9.25 kg is 0.285 N.
What's their center-to-center separation?

Explanation / Answer

n = number of people = 7.22 billion = 7.22 x 109

time = 1 year = 365 days = 365 x 24 x 3600 sec

Total energy = 2 x 103 x 7.22 x 109 (365 x 24 x 3600) = 4.5 x 1020 J

3.

r = center to center distance

m = mass of each sphere = 9.25 kg

F = force = 0.285 x 10-6 N

Using the formula

F = Gm2/r2

0.285 x 10-6 = (6.67 x 10-11) (9.25)2 / r2

r = 0.142 m

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