Understanding Telecommunication Satellites and Relative Speed

Telecommunication satellites are artificial satellites placed in orbit around the Earth. Many of these satellites, especially those used for broadcasting and long-distance communication, are placed in a special type of orbit called a geostationary orbit.

A geostationary orbit is a circular orbit around the Earth that is located directly above the Earth's equator. Satellites in this orbit have a specific altitude (approximately 35,786 kilometers above sea level) and orbit in the same direction as the Earth's rotation (west to east).

Analyzing Statement (a): Speed Relative to Earth

Statement (a) says: "The speed of telecommunication satellite relative to earth is zero."

For a satellite in a geostationary orbit, its orbital period is exactly 24 hours, which is the same as the Earth's rotation period. This means the satellite completes one orbit in the same amount of time the Earth takes to complete one rotation.

Because the satellite is orbiting at the same angular velocity as the Earth and is positioned above the equator, it stays above the same point on the Earth's surface. Therefore, its velocity relative to a point on the rotating Earth's surface is zero.

So, statement (a) is true for telecommunication satellites in geostationary orbits, which are common for this purpose.

Analyzing Statement (b): Apparent Stationarity

Statement (b) says: "Hence it appears to be stationary to a person on the earth."

If an object's speed relative to you is zero, it means its position relative to you is not changing. When a telecommunication satellite is in a geostationary orbit, it remains above the same geographical location on Earth.

For an observer on the ground, the satellite appears to hang motionless in the sky. This is why satellite dishes for receiving broadcasts from geostationary satellites can be fixed in a single direction rather than needing to track the satellite.

Therefore, statement (b) is also true, and it describes the observable consequence of statement (a).

Relationship Between Statements (a) and (b)

Statement (a) provides the physical condition (zero relative speed) that directly causes the observation described in statement (b) (appearing stationary). The word "Hence" in statement (b) suggests a causal relationship.

Because the speed of the satellite relative to Earth is zero, it consequently appears stationary to an observer on Earth. Thus, statement (a) is true, and it is the reason for statement (b) being true.

Conclusion

Based on the analysis:

• Statement (a): The speed of telecommunication satellite relative to earth is zero (for a geostationary satellite). This is true.
• Statement (b): Hence it appears to be stationary to a person on the earth. This is true, and it is a direct consequence of (a).

Therefore, statement (a) is true, and it provides the reason for statement (b).