Two solid objects, A and B, of equal mass are placed in thermal contact inside an insulated chamber. The chamber is initially at atmospheric pressure and no phase changes occur during the experiment. A probe in each object records the temperature every 15 s. A verbal description of the resulting temperature–versus–time plots is given below.
• Object A: starts at 80 °C, cools nearly linearly to 60 °C in the first 2 min, then continues to cool more gradually until reaching 50 °C at 10 min.
• Object B: starts at 20 °C, warms nearly linearly to 40 °C in the first 2 min, then continues to warm more gradually until reaching 50 °C at 10 min.
Assume both objects have the same heat capacity, and no heat is exchanged with the surroundings.
(a) Identify which object was initially at the higher temperature and state the evidence from the plots that supports your answer.
(b) Describe the direction of energy transfer between the two objects during the first 2 min. In your description, refer explicitly to the slopes of the temperature curves.
(c) Explain why the temperature curves for both objects become flatter as time approaches 10 min.
(d) At 10 min the temperature curves are nearly horizontal. Explain, on a particulate (molecular) level, what this indicates about the distribution of kinetic energies in the two objects.