InterviewSolution
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                                    57. A circular plate of uniform thickness has a diameter of 56 cm. Acircular portion of diameter 42 cm is removed from one edge of theplate. Find the centre of mass of the remaining portionAns. 9 cm from the centre of the plate. | 
                            
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Answer»  Thickness of plate = t Totalmass of circularplate = MDensity of plate = M /(πr₁² t) , r₁ = 28 cm r₂= radius of cut out part= 21 cm Mass of small circular portion cut out = volume* density =πr₂² t *(M/π r₁² t) m₂ = M r₂² / r₁² Mass of the remaining part = m3 = M - Mr₂² / r₁² = M (r₁² - r₂²) / r₁² Let the center of mass of remaining portion be at a distance d from the center of original full plate. From symmetry the center of mass of remaining portion lies along the line joining the center of original plate and the center of removed part. Let Center of mass of total full plate = 0 0 = 1/M ( d * mass of remaining part + C₁C₂ * mass of removed part) 0 = d *M (r₁² - r₂²) / r₁² + 7 * M r₂² / r₁² 0 = d * (r₁² - r₂²) + 7 *r₂² d = - 7 * r₂² / (r₁² - r₂²) = - 7 * 21² / (28² - 21²) = - 7 *21 * 21/ 49*7 = - 9 cm Center gravity of the remaining portion is 9 cm to the left of the original center of full plate on the line of symmetry. Or, it is 19 cm from the edge of remaining plate along the line of symmetry. sristi patna se ho tum kon Institute me padhti ho  | 
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