AIIMS 2007 Physics Weightlessness Assertion Reason Question

To understand the assertion and reason provided in the question, we need to analyze them carefully in the context of gravitational physics.

Assertion: An astronaut experiences weightlessness in a space satellite.

Explanation: In a space satellite, both the satellite and the astronaut inside it are in a state of free fall towards the Earth. However, they are also moving forward at such a high speed that they keep missing the Earth. This creates a condition known as orbital motion. The key point here is that because both the satellite and the astronaut are accelerating towards the Earth due to gravity, but at the same time, they are moving forward, the astronaut feels no normal force acting on them. This sensation is what we refer to as "weightlessness."

In terms of forces, the gravitational force $F$ acting on the astronaut is given by:

$$F = mg$$

where $m$ is the mass of the astronaut and $g$ is the acceleration due to gravity (approximately $9.81 \, \text{m/s}^2$ near the Earth's surface). However, since there is no contact force acting on the astronaut (the normal force is zero), the astronaut feels weightless.

Reason: When a body falls freely it does not experience gravity.

Explanation: This statement is misleading. A body that is in free fall is indeed under the influence of gravity. In fact, it experiences the full effect of gravitational acceleration. The confusion arises because, during free fall, the body does not experience a normal force acting on it (like when you stand on a scale), which is why it feels weightless.

When a body falls freely, the force of gravity is still acting on it; however, since it is not supported by any surface, it does not exert a force back (normal force). Thus, the astronaut feels weightless because they are accelerating at the same rate as the gravitational pull, not because gravity is absent.

Conclusion:

• The assertion is true because astronauts do experience weightlessness in orbit due to free fall.
• The reason is false because a freely falling body does experience gravity.

Therefore, the correct answer is:

B) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

Why Other Options are Incorrect:

• Option A: Both Assertion and Reason are true and Reason is the correct explanation of Assertion. Incorrect because the reason provided does not correctly explain the assertion.
• Option C: Assertion is true but Reason is false. Incorrect because both parts are not true; the assertion is true, but the reason is misleading and thus considered false in this context.
• Option D: Both Assertion and Reason are false. Incorrect because the assertion is true.

Key Concepts:

1. Weightlessness: Occurs in free fall when the normal force is zero.
2. Gravity: Always acts on objects, even when they are in free fall.
3. Free Fall: A state where the only force acting on an object is gravity.

In summary, understanding the distinction between experiencing gravity and feeling weightlessness is crucial in grasping concepts of gravitation and orbital mechanics.