Two slabs of equal thickness and cross-sectional area have thermal conductivities K1 and K2. If they are joined in series, the equivalent thermal conductivity of the combination is: MCQ with Answer and Explanation

Explanation:
The human ear retains the sensation of sound for about 0.1 seconds (persistence of hearing). To hear a distinct echo, the reflected sound must reach the ear after at least 0.1 s. Distance traveled by sound = Speed × Time = 344 m/s × 0.1 s = 34.4 m. Since this is the total distance (go and return), the minimum distance to the obstacle is 34.4 / 2 = 17.2 meters.

Explanation:
T = 2π√(R/g) ≈ 5076 s ≈ 84.6 min for r ≈ Earth radius. Standard result. Memory aid: 'Low orbit: ~84 min; geostationary: 24 hours'. Orbital mechanics fact frequently tested in competitive exams.

Explanation:
Pascal (Pa) named after Blaise Pascal, derived unit for pressure (N/m²). Metre, kilogram, second are base units. Joule, watt, newton, hertz, coulomb also named scientists.