Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2024/paper-1/12/b/solution

Use cylindrical coordinates about the dumbbell axis. Their Jacobian determinant contributes the volume factor , so the handle's mass is the volume integral
Inserting the radius from part (a) yields

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