400g of cold water is added to 200g of water at 70^\circC. If they are properly mixed and the temperature of the mixture is 30^\circC. calculate the initial temperature of the cold water. (Neglect the heat absorbed by the container)
A
10°C
B
15°C
C
20°C
D
30°C
E
40°C
Verified Correct Answer: A.
Physical Principles & Numerical Solution
Heat lost by the warm water = heat gained by cold water
m\(_w\) X c X ( Tw - Tm) = m\(_c\) X c X (Tm - Tc)
200 X ( 70 - 30) = 400 X ( 30 - Tc)
2 x 40 = 120 - 4Tc
4Tc = 120 - 80 = 40
Tc = \(\frac{40}{4}\) = 10ºC
Source: Myschool Past Questions Archive (Record #42717)