1. The problem statement, all variables and given/known data Problem is in attachment pic. 2. Relevant equations 3. The attempt at a solution My attempt is on the pics 1 and 2. Firstly, is it valid to assume length as 0.075m? - For part (i), from the question it infers that one of the cylinders is applicable to the lumped capacitance method, for this Bi should be less than 0.1, although only cylinder is 0.15 which is the lowest. Bt I will assume that this is the one because the question asks to use the cylinder in which lumped capacitance works. - In my working for part (i), I have calculated the temperature after 30mins, but the question asks for the temperature at the AXIS and at the SURFACE of the cylinder. So I am a little confused on how to go about with this - For part (ii), is the way I calculated amount of energy per unit length released by cylinder in 30mins of cooling correct? Also it says there are two methods, has anyone got any idea on what the second method could be Thanks alot!