Questions
GEOL0012_25-26 **********GEOL0012 Moodle Test (unassessed) 2025/26**********
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Question text1. The water volume of the Aral sea was 1093 km3[math] in 1960, and decreased exponentially to 102 km3[math] in 2009. The density of salty water is about 1020 kg/m3[math]. a) Calculate the mass of water lost by the Aral sea from 1960 until 2009. Approximate your answer to 3 significant figures and give the answer in kg. Answer 1 Question 7[input] ×1015kg[math] b) Assume that the mass of the lost water was 9.09×1014[math] kg and that it was evaporated and redistributed over the surface of Earth as a homogeneous thin spherical shell. This change in mass distribution will result in a change in Earth’s moment of inertia. Assume that initially the lake had all its mass concentrated at a point with coordinates 45°N 60°E (a point mass approximation). Calculate the change in Earth’s moment of inertia due to the redistribution of Lake Aral’s water. Give the answer in kgm2[math] to 3 significant figures (be careful with the sign of the final answer). You may use: -Moment of inertia of homogeneous thin spherical shell with mass M and radius R is: I=(2/3)MR2[math] -Moment of inertia of point mass with mass M and distance r from axis of rotation is: I=Mr2[math] -Radius of Earth=6371 km Answer 2 Question 7[input] ×1027kgm2[math]c) Assume the moment of inertia of Earth in 1960 to be 8.04×1037kgm2[math] and that the change in moment of inertia due to Aral's water evaporation was 6.77×1027kgm2[math]. Conservation of angular momentum tells us that: Iinitial/Tinitial=Ifinal/Tfinal[math] Where I[math] and T[math] are the moment of inertia and Earth’s period of rotation about its own axis (24 hours). Calculate in microseconds the expected change in Earth’s rotation period. Approximate to 2 significant figures.Answer 3 Question 7[input] μs[math]

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To tackle this multipart problem, I will examine each sub-question (a, b, c) in turn and explain why the given numeric choices are reasonable, while showing the underlying physics and unit conversions that lead to those values.
Option a) mass lost by the Aral Sea
- The change in volume is from 1093 km^3 to 102 km^3, so the net loss is 1093 − 102 = 991 km^3. This is the volume of water that evaporated/was lost.
- Convert to cubic meters: 991 km^3 = 991 × 10^9 m^3.
- With density ρ ≈ 1020 kg/m^3, the corresponding mass lost is M = ρ × volume ≈ 1020 × 991 × 10^9 kg.
- Computing gives M ≈ 1.012 × 10^15 kg, which rounds to 1.01 × 10^15 kg when keeping three significant figures. This aligns with the provided value, indicating the mass-loss calculation is consistent with the inputs.
- In short, the reasoning uses a straightforward volume-diff......Login to view full explanationLog in for full answers
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Question text1. The water volume of the Aral sea was 1093 [math: km3] in 1960, and decreased exponentially to 102 [math: km3] in 2009. The density of salty water is about 1020 [math: kg/m3]. a) Calculate the mass of water lost by the Aral sea from 1960 until 2009. Approximate your answer to 3 significant figures and give the answer in kg. Answer 1 Question 7[input] [math: ×1015kg] b) Assume that the mass of the lost water was [math: 9.09×1014] kg and that it was evaporated and redistributed over the surface of Earth as a homogeneous thin spherical shell. This change in mass distribution will result in a change in Earth’s moment of inertia. Assume that initially the lake had all its mass concentrated at a point with coordinates 45°N 60°E (a point mass approximation). Calculate the change in Earth’s moment of inertia due to the redistribution of Lake Aral’s water. Give the answer in [math: kgm2] to 3 significant figures (be careful with the sign of the final answer). You may use: -Moment of inertia of homogeneous thin spherical shell with mass M and radius R is: [math: I=(2/3)MR2] -Moment of inertia of point mass with mass M and distance r from axis of rotation is: [math: I=Mr2] -Radius of Earth=6371 km Answer 2 Question 7[input] [math: ×1027kgm2]c) Assume the moment of inertia of Earth in 1960 to be [math: 8.04×1037kgm2] and that the change in moment of inertia due to Aral's water evaporation was [math: 6.77×1027kgm2]. Conservation of angular momentum tells us that: [math: Iinitial/Tinitial=Ifinal/Tfinal] Where [math: I] and [math: T] are the moment of inertia and Earth’s period of rotation about its own axis (24 hours). Calculate in microseconds the expected change in Earth’s rotation period. Approximate to 2 significant figures.Answer 3 Question 7[input] [math: μs]
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