Plan your route before writing. Use equations, diagrams, units, and a clear final justification where needed.
A student investigates energy transfer between a hot metal block and a liquid.
An aluminium block of mass $0.200\,\mathrm{kg}$ is heated from $20.0\,^{\circ}\mathrm{C}$ to $100.0\,^{\circ}\mathrm{C}$. The heater is then removed. The dry block is placed completely into a cup containing $0.100\,\mathrm{kg}$ of water, initially at $20.0\,^{\circ}\mathrm{C}$.
The water is stirred gently until the block and water reach the same temperature.
Use the following data:
specific heat capacity of aluminium: $900\,\mathrm{J\,kg^{-1}\,K^{-1}}$
specific heat capacity of water: $4200\,\mathrm{J\,kg^{-1}\,K^{-1}}$
For parts (a) and (b), assume that the specific heat capacities are constant, no energy is lost to the surroundings, and the cup, thermometer and stirrer absorb negligible energy. The block is still at $100.0\,^{\circ}\mathrm{C}$ when it enters the water. No material changes state and no water is lost.
(a)
2 marks
Calculate the energy transferred to the aluminium block as it is heated from $20.0\,^{\circ}\mathrm{C}$ to $100.0\,^{\circ}\mathrm{C}$.
(b)
4 marks
Calculate the common final temperature of the aluminium block and the water. Show how conservation of energy is used in your calculation.
(c)
2 marks
In the real experiment, the room is at $20.0\,^{\circ}\mathrm{C}$. Some energy is transferred to the surroundings while the hot block is moved and while the water is stirred. Continue to neglect energy absorbed by the cup, thermometer and stirrer.
State whether the temperature recorded when the block and water first reach the same temperature will be higher than, lower than, or equal to your answer to (b). Explain your answer in terms of energy transfer.
(d)
2 marks
Suggest one practical change that would reduce energy transfer to the surroundings during this experiment. Explain how your change would help.
