Problem 3

In an insulated vessel,

m_h=0.40\,\mathrm{kg}

of water at

60^\circ\mathrm C

is mixed with

m_c=0.20\,\mathrm{kg}

of water at

30^\circ\mathrm C

. Water has specific heat

c=4200\,\mathrm{J\,kg^{-1}K^{-1}}

; neglect the vessel heat capacity and heat loss. After mixing, the water reaches one uniform final temperature, with no evaporation or phase change. Heat is exchanged only between the two portions of water; the insulated vessel takes up no energy. Define heat as positive when the portion considered gains energy and negative when it loses energy. (a) Find the equilibrium temperature

T_f

. (b) Calculate the signed heat transferred by the hot water. (c) Find the heat received by the cold water and check energy conservation. (d) State the ordering of

T_c,T_f,T_h

problems.proof.stepOf

problems.proof.prevStep problems.proof.nextStep

m_hc(T_h-T_f)=m_cc(T_f-T_c)

problems.proof.analysis

The vessel is insulated, so the heat lost by the hot portion equals the heat gained by the cold portion. Both portions are liquid water with the same specific heat, which cancels.