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1.3 Derive the continuity equation from first principles using an infini- tesimal control volume of spherical shape and having dimensions (or, r80, rsino 80). Identify the net mass flow rate through each surface of this element as well as the rate at which the mass of the element is increasing. The resulting equation should be expressed in terms of the spherical coordinates (1,0,0,t), the spherical velocity compo- nents (u UU.), and the fluid density p. 1.4 Obtain the