An artificial satellite is revolving around earth. The physical quantity which is conserved is

Options

A. angular momentum
B. torque
C. moment of Inertia
D. Total energy

Answer

To solve the question regarding the physical quantity that is conserved for an artificial satellite revolving around the Earth, we can follow these steps:

### Step 1: Understand the Motion of the Satellite
An artificial satellite moves in a circular or elliptical orbit around the Earth due to the gravitational force acting on it. This force provides the necessary centripetal force for the satellite's motion.

**Hint:** Consider the forces acting on the satellite and how they relate to its motion.

### Step 2: Identify the Relevant Physical Quantities
The question asks which physical quantity is conserved. The options given are:
- Angular momentum
- Torque
- Moment of inertia
- Total energy

**Hint:** Think about the principles of conservation laws in physics, particularly in orbital mechanics.

### Step 3: Analyze Angular Momentum
Angular momentum (\(L\)) for a satellite can be expressed as:
\[ L = mvr \]
where \(m\) is the mass of the satellite, \(v\) is its tangential velocity, and \(r\) is the radius of the orbit. In the absence of external torques, angular momentum remains constant.

**Hint:** Recall that in a closed system with no external torques, angular momentum is conserved.

### Step 4: Consider Torque
Torque (\(\tau\)) is defined as the rate of change of angular momentum. If there are no external forces acting on the satellite (other than gravity), the net torque is zero, which implies that angular momentum is conserved.

**Hint:** Think about how torque relates to forces and motion in a circular path.

### Step 5: Evaluate Moment of Inertia
Moment of inertia (\(I\)) depends on the mass distribution of the satellite and its distance from the axis of rotation. While the moment of inertia can change if the satellite's mass distribution changes, it does not directly relate to the conservation in this scenario.

**Hint:** Consider how moment of inertia changes with mass distribution and whether it is conserved in this context.

### Step 6: Assess Total Energy
Total mechanical energy (kinetic + potential) of the satellite can also be considered. While energy is conserved in an isolated system, the total mechanical energy of the satellite can change due to gravitational potential energy changes as it moves in its orbit.

**Hint:** Think about how energy can be transformed but not necessarily conserved in all forms.

### Conclusion
The physical quantity that is conserved for an artificial satellite revolving around the Earth is **angular momentum**. Therefore, the correct answer is angular momentum.

### Final Answer
**Angular momentum is conserved for an artificial satellite revolving around the Earth.**

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