UPSC Prelims 2002 · General Studies

Question 147: Science and Technology

Assertion (A): Artificial satellites are always launched from the earth in the eastward direction. Reason (R): The earth rotates from west to east and so the satellite attains the escape velocity.

aBoth A and R are individually true and R is the correct explanation of A

bBoth A and R are individually true but R is not a correct explanation of A

cA is true but R is false

dA is false but R is true

AnswerThe answer is (c).

Assertion A is true: satellites are launched towards the east because the Earth's rotation, about 0.46 km/s at the equator, adds to the rocket's speed and saves fuel. Reason R is false: a satellite needs orbital velocity (about 7.9 km/s near the surface), not escape velocity (11.2 km/s), and the Earth's rotation helps by adding to it. Polar orbits are launched north or south, so 'always' is a little too strong, but the key accepts A.

A. Eastward launches use the Earth's rotation to save fuel.
R. Satellites need orbital velocity, not escape velocity.

How you could have got this

If you were sure statement 1 is correct, (d) goes. Then judge the second statement; if it is correct too, decide whether it explains the first.

This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.

Which options go is worked out from UPSC’s key and the options, not by a model.

Why each option is right or wrong

(a) R is false, so it cannot be the explanation.
(b) R is false, so this option fails.
(c) Right: A is true and R is false.
(d) A is accepted as true, so this option fails.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2002, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.