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(1) The block of wax below has a spatially uniform temperature. The bottom surface is uniformly heated with constant flux qe', using a very thin heating tape. The top surface is exposed to flow at the leading edge as shown, and the flow is observed to be laminar over the entire length. The velocity of the flow increases with time: u.(t) = Et, where E is a constant. The wax is softening, such that its density changes with time: Ps(t) = Bt, where B is a constant. Its volume and all other properties do not change with time. Vy, Psykt, Cpf Fluid only contacts top surface = Et (Laminar flow) ) TO U..(t) = 1991 Solid Spatially uniform T H Vs, ks, Cp, Ps(t) = Bt = Initially at temperature Ti L w qe applied uniformly (Thin heating tape) (a) What is the criterion for assuming that the temperature within the solid wall is spatially uniform? What is this assumption called? (b) Assume the criterion in (a) is met. Derive an expression for the temperature of the block as a function of time, using only variables in the diagram, if the block is initially at temperature Ti.