Heat capacity — UPSC CSE 2022 Physics PYQ

A body of constant heat capacity C_p and a temperature T_i is put into contact with a reservoir at temperature T_f. Equilibrium between the body and the reservoir is established at constant pressure. Determine the total entropy change and prove that it is positive for either sign of \left[(T_f-T_i)/T_f\right]. Consider \left|\frac{T_f-T_i}{T_f}\right|<1.