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physics A-Level Physics
 
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Gravitational Force Between Point Masses

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Example 1.

Two iron balls with radii of 6 and 10 cm are in contact. What is the attractive force between them? The density of iron is .

    
Example 2.

The Sun, Earth, and Moon form a right triangle with the shortest and longest sides of lengths 380,000 km and 150 million km respectively. What is the resultant of the gravitational forces on the Moon? The mass of the Earth is , the mass of the Sun is 330,000 times that of the Earth, and the mass of the Moon is one-eighty-first that of the Earth.

    
3.

Where between the Earth and the Moon is the resultant of the gravitational forces of both bodies zero? The distance between the Earth and the Moon is 380000 km, the mass of the Earth is , and the mass of the Moon is .

    
4.

What is the gravitational acceleration on the Moon? The radius of the Moon is 1730 km and its mass is . What is the weight of an astronaut on the Moon if his mass on Earth is 100 kg?

    
5.

A comet is trapped in a strongly elliptical orbit around the Sun. What is the distance of the comet from the Sun at the moment when they are farthest apart if we know that the comet needs 15 months for one complete revolution and the average distance of the Earth from the Sun is ?

    
6.

A satellite orbits the Earth at a lower altitude above the equator. This means that the height h is much smaller than the radius of the Earth. How long does it take for a satellite to reach the same position above the Earth if we launch it towards the east? The radius of the Earth is 6370 km.

    
7.

Planet Mars is from the Sun. How long does it take to go round the Sun? Kepler's constant is .