A man pushes a wall but fails to move it. He does MCQ with Answer and Explanation

Explanation:
The gravitational potential V inside a uniform solid sphere at a distance r from the center is V = -GM * (3R^2 - r^2) / (2R^3). At the exact center of the Earth, r = 0. Substituting r = 0 gives V = -GM(3R^2) / 2R^3 = -3GM / 2R. The potential is strictly non-zero and highly negative.

Explanation:
Least count determines precision: two decimal places. So 2.50 cm. Extra digits indicate false precision.

Explanation:
Electron mass 9.11×10⁻³¹ kg, proton ~1.67×10⁻²⁷ kg.