A hot iron ball is dropped into a $100 \text{ g}$ sample of water initially at $30^\circ$C. If 4.2 kJ of heat is transferred from the ball to the water, what is the final temperature of the water? (The specific heat of water is $\pu{4.2 J/(g.^\circ \text{C})}$.)

Summary Submit Skip Question

The heat transferred by the iron ball to the water.

$$q_{\text{lost}}=q_{\text{gained}}$$ $$\pu{4.2 kJ} = mc\Delta T$$ $$\pu{4,200 } = 100(4.2)(T_f-30)$$ $$10 = T_f -30$$ $$T_f = \boxed{40}$$