Let us assume that our galaxy consists of 2.5 × 1011 stars each of one solar mass. How long will a star at a distance of 50,000 ly from the galactic centre take to complete one revolution? (The diameter of the milky way is 105 ly.)
1. 3.55 × 108 years
2. 4.55 × 108 years
3. 3.55 × 107 years
4. 4.55 × 107 years

Subtopic:  Satellite |
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A satellite orbits the earth at a height of 400 km above the surface. How much energy must be expended to rocket the satellite out of the earth’s gravitational influence? (Mass of the satellite = 200 kg; mass of the earth = 6.0×1024 kg, radius of the earth = 6.4 × 106 m, G = 6.67 × 10-11 N m2 kg-2)

1. 7.5 × 109 J
2. 4.7 × 109 J
3. 4.4 × 109 J
4. 5.9 × 109 J

Subtopic:  Satellite |
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