The speed of sound in air at 0°C is approximately MCQ with Answer and Explanation

Explanation:
Average Earth-Sun distance (1 AU) ≈ 1.5×10¹¹ m. Speed of light c = 3×10⁸ m/s. Time t = distance/speed = 1.5×10¹¹ / 3×10⁸ = 500 seconds ≈ 8.33 minutes ≈ 8 minutes. This is a standard astronomical fact. Memory aid: 'Sunlight takes 8 minutes to reach Earth; we see the Sun as it was 8 minutes ago'. This factual knowledge question tests awareness of scale in physics, frequently appearing in competitive exams. Always recall key constants: Earth-Sun distance, light speed, for quick estimations.

Explanation:
A geostationary satellite orbits the Earth directly over the equator at an altitude of ~35,786 km. It revolves in the same direction the Earth rotates. Its orbital period perfectly matches Earth's rotational period, which is 24 hours. Because of this, it appears entirely stationary from any point on Earth's surface, making it ideal for communications and DTH TV.

Explanation:
Heavy water (D₂O) slows neutrons, good moderator.