UPSC Prelims 2011 · GS Paper I

Question 81: Science and Technology

An artificial satellite orbiting around the Earth does not fall down. This is so because the attraction of Earth

adoes not exist at such distance

bis neutralized by the attraction of the moon

cprovides the necessary speed for its steady motion

dprovides the necessary acceleration for its motion

AnswerThe answer is (d).

A satellite is in free fall around the Earth. Gravity keeps pulling it, and that pull provides the centripetal acceleration that bends its path into a circle or an ellipse around the Earth. Its sideways speed is large enough that the ground curves away as fast as the satellite falls, so it never comes down. Gravity does not vanish at that height, is not cancelled by the moon, and does not itself give the speed; it gives the acceleration.

Why each option is right or wrong

(a) Earth's attraction still acts at satellite heights; it is weaker but present.
(b) The moon's pull does not neutralise Earth's gravity.
(c) Gravity gives acceleration, not speed; the speed comes from the launch.
(d) Right: Earth's attraction supplies the centripetal acceleration for the orbit.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2011, General Studies Paper I, Series A. The paper on upsc.gov.in.