The weight of a body at Earth's centre is MCQ with Answer and Explanation

Explanation:
Parallel-faced slab: refraction at entry and exit cancel angular deviation, but ray shifts laterally. No net direction change. Memory tip: 'Slab: parallel emergent ray; Prism: deviated emergent ray'. Ray optics concept frequently tested in competitive exams.

Explanation:
KE = p²/2m. If p → 2p, KE' = 4KE, increase = 3KE = 300%. Frequently asked.

Explanation:
a = (0-20)/4 = -5 m/s². s = 20×4 + ½(-5)×16 = 80 - 40 = 40 m. Or average velocity 10 m/s × 4 = 40 m.