JEE MainPhysicsGravitationMCQ+4 / −1
A satellite is moving in a low nearly circular orbit around the earth. Its radius is roughly equal to that of the earth’s radius Re . By firing rockets attached to it, its speed is instantaneously increased in the direction of its motion so that it become times larger. Due to this the farthest distance from the centre of the earth that the satellite reaches is R. Value of R is :
- A2Re
- B3Re
- C4Re
- D2.5Re
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Correct answer: B
- Initial circular orbit
The satellite is in a low circular orbit of radius approximately equal to Earth's radius:
For a circular orbit, speed is where is the mass of Earth.
- Speed after firing rockets
Its speed is increased instantaneously in the same direction to So,
- Nature of the new orbit
The velocity is increased tangentially, so the point where the impulse is given becomes the perigee (nearest point), since speed there is maximum.
Thus, Let the farthest distance be .
- Use conservation of mechanical energy
Total specific energy (energy per unit mass) just after the impulse is Substitute :
For an elliptical orbit, where is the semi-major axis.
So, Cancel :
- Relate semi-major axis to nearest and farthest distances
For an ellipse, Thus,
- Check options
- A: ❌
- B: ✅
- C: ❌
- D: ❌
Therefore, the farthest distance from the center of Earth is
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