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Motion In Straight Line

Question
CBSEENPH11026322

The density of a rod having length l varies as ρ = c + dx, where x is the distance from the left end. The centre of mass is     

  • 3 cl + 2 D l23  2c + D l 

  • 2 cl + 3D I22  4c + 8I 

  • 2 cl + 3 DI23 2c + I

  • cl + DI22  2 c + DI 

Solution

A.

3 cl + 2 D l23  2c + D l 

Let the cross-sectional area is α. The mass of an element of length dx located at a distance x away from the left end is (C + Dx)α dx.  The x-coordinate of the centre of mass is given by

         Xcm =  x cm dm

               = 0lxC + Dx  α dx0l C + Dx  α dx

Where limit is from 0 to l.

              = C l22+ D l3Cl + D l22 

             Xcm3 CI + 2 DI23 2C + DI