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1. A circular plate of uniform thickness has a diameter56 cm. A circularportion of diameter 42cm is removed from oneedge as shown in thefigure. The centre of omass of the remainingportion from the centreof plate will be28 cm

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.



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