Past exam of the physics B course of the University of Cambridge / 2015 / Paper 2 / Section A / A1

For entropy gain from impact and thermal equilibration, let the large lake be a reservoir at an initially unspecified temperature $T_L$, in kelvin, and take the final meteorite temperature to be $T_L$. Its initial temperature is $T_i=1273.15\mathrm{K}$. The meteorite loses thermal energy $mc(T_i-T_L)$, and its kinetic energy $m{v}^2/2$ is also dissipated into the lake. ThusandBoth heat equilibration and dissipation contribute positively. For the requested estimate, assume a lake temperature $T_L=300\mathrm{K}$. This gives $\Delta S_{\mathrm{universe}}\simeq 2.93\times 10^3\mathrm{J}{\mathrm{K}}^{-1}$. Taking $273$–$300\mathrm{K}$ instead gives about $3.3$–$2.9\mathrm{kJ}{\mathrm{K}}^{-1}$; this shows the estimate's sensitivity without asserting an unprovided lake temperature. The boxed expression retains the full temperature dependence. The model uses the stated constant heat capacity, no phase change of the meteorite, and a lake large enough that its temperature change is negligible.^[ref]