UPSC Prelims 2002 Q147: Science & Technology – Space Technology & Astronomy
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.
- (a) Both A and R are individually true and R is the correct explanation of A
- (b) Both A and R are individually true but R is not a correct explanation of A
- (c) A is true but R is false
- (d) A is false but R is true
Answer: (c) A is true but R is false
Explanation
Assertion-Reason: launching satellites eastward
| Statement | Verdict |
|---|---|
| Assertion: satellites are always launched eastward | True in general — eastward launch uses the Earth's rotation |
| Reason: the Earth rotates west to east so the satellite attains escape velocity | False — the rotation gives a speed boost; the satellite does not attain escape velocity |
| Orbit speed | A satellite needs orbital velocity (about 7.9 km/s), far below escape velocity (11.2 km/s) |
| Result | A is true but R is false |
Launching eastward adds the Earth's surface speed (about 0.46 km/s at the equator) to the rocket, saving fuel. But a satellite does not reach escape velocity; if it did, it would leave the Earth's gravity. So A is true and R is false.
Answer: (c) A is true but R is false.
Why each option is right or wrong
- (a) Incorrect. R wrongly says the satellite attains escape velocity.
- (b) Incorrect. R is false because escape velocity is not attained.
- (c) CORRECT. A is true; R is false, as satellites do not reach escape velocity.
- (d) Incorrect. A is true; launches are mostly eastward.
Key point
Orbital velocity about 7.9 km/s at low orbit; escape velocity 11.2 km/s; polar launches go north-south.
Remember
Eastward launch adds Earth's rotation speed; no escape velocity needed.
Common mistakes
- Mixing orbital velocity with escape velocity.
- Thinking eastward launches are the only possible ones.
- Accepting R because it sounds scientific.
Exam tip
A satellite stays bound to Earth, so it cannot have escape velocity.
Sources
- NCERT Class XI Physics — Gravitation
- ISRO — launch basics