question_answer 27)

                  As observed from earth, the sun appears to move in an approximate circular orbit. For the motion of another planet like mercury as observed from earth, this would                 (a) be similarly true.                 (b) not be true because the force between earth and mercury is not inverse square law.                 (c) not be true because the major gravitational force on mercury is due to sun.                 (d) not be true because mercury is influenced by forces other than gravitational forces.

Answer:

                  (c, d) As observed from the Earth, Sun appears to move around the Earth in a circular orbit though in reality Earth moves around the Sun due to gravitational force between them. All planets move around the Sun due to huge gravitational force of the Sun acting on them. The gravitational force on Mercury due to Earth is much smaller as compared to that acting on it due to Sun and hence it resolves around the Sun and not around the Earth.