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Q61. Shear strain is measured by changes in:
Shear strain deforms the shape of a body without necessarily changing its volume or length. It is mathematically defined as the change in the angle between two originally perpendicular lines.
Q62. The correct increasing order of compressive strength of Earth materials is:
Shale (a foliated mudrock) has very low compressive strength. Sandstone is intermediate, and Gabbro (a dense, crystalline, intrusive igneous rock) has the highest compressive strength of the three.
Q63. S waves move faster through gabbro than granodiorite because:
Seismic velocity depends on stiffness (modulus) and density. Although gabbro is denser (which usually slows waves), its high stiffness (shear modulus) overcompensates, making S-waves faster.
Q64. Compressional wave velocity is the highest in:
Seismic P-wave velocity generally increases with the density and rigidity of the rock. Ultramafic rocks like Dunite (>8.0 km/s) support much faster wave propagation than mafic or felsic rocks.
Q65. Which one of the following does not form ultimate or temporary base level of subaerial erosion?
Sea level is the ultimate base level. Dams and lakes act as temporary local base levels where streams deposit sediment. A tributary is just a smaller feeder stream, not a base level.
Q66. A planet is identical to the Earth in all respects except that its atmospheric composition is purely oxygen (instead of Earth's 80:20 mixture of nitrogen and oxygen). The scale height of such an atmosphere relative to that of the Earth is expected to be:
Scale height is inversely proportional to the mean molecular weight of the atmosphere. Earth's average molecular weight is ~28.8 (80% N2 at 28, 20% O2 at 32). Pure oxygen is 32. The ratio is 28.8 / 32, which simplifies to 0.9 or (7.2/8).
Q67. If the Earth's atmosphere were made of H2, what would be the scale height of such an atmosphere? (km)
Scale height (H = RT/Mg) is inversely proportional to molar mass. Earth's N2/O2 mass is ~29 g/mol (H=8.5km). H2 mass is 2 g/mol. Ratio is 14.5. New scale height = 8.5 * 14.5 = ~123 km (closest is 120 km).
Q68. Which of the following rocks is not expected to occur on the moon?
Sandstone is a sedimentary rock that requires water transport, weathering, and deposition processes, which do not exist on the Moon.
Q69. A granite block is subjected to external load at room temperature, but it does not show any visible crack. The reason is:
Rocks will not undergo brittle failure (cracking) unless the applied stress exceeds their elastic limit (yield/ultimate strength).
Q70. The magnitude of an earthquake is determined from:
Richter magnitude is calculated specifically using the logarithm of the maximum amplitude of seismic waves (horizontal ground motion) recorded by a seismograph, corrected for distance.