BPSC CCE Prelims
Gravitation Previous Year Questions (PYQs)

Detailed Explanation:

The Moon lacks an atmosphere because its escape velocity (2.38 km/s) is lower than the root mean square (rms) velocity of gas molecules like hydrogen and helium (1–1.5 km/s).

When the rms velocity exceeds escape velocity, gas molecules possess enough kinetic energy to overcome the Moon's weak gravitational pull and escape into space. In contrast, Earth's escape velocity (11.2 km/s) is sufficiently high to retain atmospheric gases.

Detailed Explanation:

Earth's rotation creates a centrifugal effect that opposes gravity, reducing the effective weight of objects, especially at the equator where the rotational radius is maximum.

• Apparent gravity formula: g' = g - ω²R, where ω is angular speed and R is Earth's radius at the equator.
• Increased spinning speed: Higher ω increases ω²R, thereby decreasing g' (apparent gravity).
• Weight reduction: Since weight = mg', a smaller g' directly reduces the body's weight at the equator.
• Therefore, faster Earth rotation decreases equatorial weight, making Option 1 the correct answer.