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Mechanical Properties Of Solids

Question
CBSEENPH11020504

A solid sphere of radius r made of a soft material of bulk modulus K is surrounded by a liquid in a cylindrical container. A massless piston of the area a floats on the surface of the liquid, covering an entire cross section of cylindrical container. When a mass m is placed on the surface of the piston to compress the liquid, the fractional decrement in the radius of the sphere, (dr/r), is

  • mg/Ka

  • Ka/mg

  • Ka/3mg

  • mg/3Ka

Solution

D.

mg/3Ka

Bulk modulus, K = Volumetric stressVolumetric strainK= mgadVV  dVV = mgKa ....(i)Volume of sphere,V = 43πR3Fractional Change in volume dVV = 3drr .... (ii)Using equ (i) & (ii) 3drr = mgKa drr = mg3Ka (fractional decrement in radius)