Question

A thermos bottle containing 250g of Coffee at 90°C is added with a 20g of milk at 5°C. After thorough mixing, what is the final temperature. Capacity for water, coffee and milk is 1.00Cal/g°C

Answer 1

From the conservation of energy:

$$Q_c=Q_m$$

$$m_c c (T_c-T)=m_m c (T-T_m)$$

$$m_c (T_c-T)=m_m (T-T_m)$$

$$250 (90-T)=20 (T-5)$$

$$T=83.7°C$$