Question

quando misturamos 1,0 kg de agua( calor específico sensível =1,0 cal/g°C) a 70° com 2,0kg de agua a 10°C, obtemos 3,0kg de agua a:

Answer 1

1kg = 1000g
2kg = 2000g

Q1 + Q2 = 0

1000 * 1 * (TF - 70) + 2000 * 1 * (TF - 10) = 0

1000TF - 70.000 + 2000TF - 20.000 = 0

3000TF - 90.000 = 0

3000TF = 90.000

3TF = 90

TF = 90/3

TF = 30°C (Temperatura após a mistura)
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Answer 2

tf=temperatura final 
1000g=1Kg
2000g=2Kg
m=massa 
c=calor sensível
ΔT=variação da temperatura 

∑Q=0
Q=m.c.ΔT
1000.1.(tf-70)+2000.1.(tf-10)=0
1000.tf-70000+2000.tf-20000=0
3000.tf-90000=0
3000.tf=90000
tf=90000/3000
∴ tf = 30ºC