The boy filled a glass with boiling water, pouring it 150 g, and then added 50 g

The boy filled a glass with boiling water, pouring it 150 g, and then added 50 g of water at a temperature of 20 ° C. Determine the temperature that has settled in the glass.

Initial data: m1 (mass of boiling water) = 150 g = 0.15 kg; t1 (boiling water temperature) = 100 ºС; m2 (mass of cool water) = 50 g = 0.05 kg; t2 (cool water temperature) = 20 ºС.

Let’s compose an equation for calculating the steady-state water temperature:

C * m1 * (t1 – t) = C * m2 * (t – t2).

m1 * (t1 – t) = m2 * (t – t2).

Substitute all known values:

0.15 * (100 – t) = 0.05 * (t – 20).

15 – 0.15t = 0.05t – 1.

0.2t = 16.

t = 16 / 0.2 = 80 ºС.

Answer: The water temperature will be set in the glass to 80 ºС.