The bulk modulus of a spherical object is 'B’.  If it is subjected to uniform pressure ‘p’, the fractional decrease in radius is

Bulk modulus  B  is given as B=-pVΔV          ....(i)The volume of a spherical object of radius  r  is given as V=43πr3,  ΔV=43π3r2Δr∴  VΔV=43πr343π3r2Δr or VΔV=r3ΔrPut this value in eqn. (i), we get B=pr3Δr Fractional decrease in radius is -Δrr=p3B