Explanation:
Linear expansion formula: ΔL = L₀αΔT, where ΔT = T - T₀. Thus new length L' = L₀ + ΔL = L₀[1 + α(T - T₀)]. Option A incorrectly uses absolute temperature T instead of temperature change. Option C gives only the change, not total length. Option D uses initial temperature incorrectly. Memory aid: 'Expansion depends on temperature change, not absolute value'. This standard formula application is common in thermal physics questions. Always identify initial length and temperature reference point to avoid sign errors.
Explanation:
Myopia (nearsightedness) is the inability to see distant objects clearly, with far point less than infinity. Here, far point is 2 m. Corrected using concave lens. Hypermetropia (farsightedness) affects near vision; presbyopia is age-related loss of accommodation; astigmatism involves uneven corneal curvature. Memory aid: 'Myopia = near-sighted; far point reduced'. This application question tests knowledge of vision defects and corrections, frequently appearing in competitive exams. Always link symptom (blurred distant vision) to defect (myopia) and correction (diverging lens).
Explanation:
Speed = distance/time = 100 m / 5 s = 20 m/s. Convert to km/h: multiply by 18/5 => 20 × 18/5 = 72 km/h. Pole is a point, so train's own length is the distance crossed. Speed in km/h = m/s × (18/5). 20 × 18/5 = 72.
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