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When considering only the Sun, Earth, Mercury, and Mars in a planetary system, which...

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juniormax | Student, Undergraduate | (Level 1) Honors

Posted December 6, 2009 at 8:39 PM via web

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When considering only the Sun, Earth, Mercury, and Mars in a planetary system, which statement is correct?

Multiple Choice:

A) The Sun, Earth, Mars, and Mercury all go around each other with the same angular momentum.

B) At night the Sun stops until morning and then goes around the Earth during daytime only.

C) At night the Earth stops until morning and then goes around Sun during daytime only.

D) Mars goes around the Earth, but Mercury doesn't go around the Earth since its orbit is smaller

E) Mars goes around the Sun in the opposite angular direction from Mercury

F) Mars and Mercury go around the Earth.

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belarafon | High School Teacher | (Level 2) Educator Emeritus

Posted July 30, 2012 at 10:03 PM (Answer #1)

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I have no idea where those multiple choice questions could have come from or how they could not contain the only true answer: (G) Any existing planets will orbit the largest gravitational body in the Solar System, which in this scenario is still the Sun. There is no situation where one body would stop orbiting "until morning" or in which the Sun could orbit the Earth; gravity, physics, and the accepted laws of science forbid it. A planet cannot stop its orbit without encountering a force greater than its own orbit speed, which would utterly destroy the planet as the structure could not withstand that sort of impact. While the loss of the Outer Planets may cause some small changes in gravity and tides on Earth, removing them would likely have such a small effect that it would be unnoticable. The remaining planets would continue in their orbits, since no change in the greatest gravity well -- the Sun -- has occurred.

http://curious.astro.cornell.edu/question.php?number=481/

Sources:

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neela | High School Teacher | (Level 3) Valedictorian

Posted December 6, 2009 at 11:33 PM (Answer #2)

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All the statements are wrong, and at best create confusion.

Each of the planets mentioned revolve around the sun in an elliptical orbit , with sun at one of the focii of their orbit. The Sun, Mercury, Venus, Earth and Mars are in the inseasing order of the distance from the Sun.

The motion of the planets are governed by Kepler's Laws  motion , which are derivable by Newtons universal gravitational law. The radius vector joining the planet and the sun sweeps (or covers) equal area in equal intervals of time. Planets not only orbit around the sun, but also spin around their own axis. The square of period of the planet is directly proportional to the cube of the distance of the planet from the sun.

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