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Water of mass 150g at 60oc is added to 300g of water...

Water of mass 150g at 60oc is added to 300g of water at 20oc and the mixture is well stirred. Calculate the temperature of the mixture.(neglect heat losses to the surroundings)

A.

33oc

B.

40oc

C.

25oc

D.

10oc

Correct answer is A

Water 1 => M = 150g = 0.15kg,

  θ2 = 60oC; θ1 = θ

  Q1 = MC (θ2 – θ1)

  = 0.15C (60 - θ)

  Water 2 => M = 300g = 0.3kg

  θ1 = 20oC, θ2 = θ

  Q2 = MC (θ2 – θ1)

  = 0.3C (θ – 20)

  Combining Q1 and Q2

  0.15C (60 - θ) = 0.3C (θ – 20)

  9 – 0.15θ = 0.3θ – 6

  0.3θ + 0.15θ = 9 + 6

  0.45 θ = 15

  θ = 33.33oC