Question

1. an artist is using wooden cubes to build a statue. yesterday, she placed one wooden cube on the statue, and today she is going to put an identical wooden cube on top of it. both cubes are the same size and have the same number of molecules. the diagram above shows the cubes now, before they are touching. use the information in the diag answer the question.

how does the temperature of the top cube compare with the temperature of the bottom cube now, and what will happen when the cubes have been touching for a while?

a before the cubes touch, the bottom cube is hotter than the top cube. once the cubes are touching, the cooler top cube will gain kinetic energy until the molecules of both cubes have an energy of 14, because hotter things increase the temperature of cooler things.

b before the cubes touch, the bottom cube is hotter than the top cube. once the cubes are touching, the bottom cube will transfer kinetic energy to the molecules in the cooler top cube until both cubes reach the same temperature, which will be in between their starting temperatures.

c before the cubes touch, the bottom cube is cooler than the top cube. once the cubes are touching, the top cube will transfer kinetic energy to the molecules in the cooler bottom cube until both cubes reach the same temperature, which will be in between their starting temperatures.

d before the cubes touch, the two cubes are different temperatures. once the cubes are touching, both kinetic energy and cold energy will transfer between the molecules in the two cubes until both cubes reach the same temperature, which will be in between their starting temperatures.

Explanation:

First, temperature is related to the average kinetic energy of molecules. The bottom cube has higher average molecular kinetic energy (sum of molecule energies: 12+14+16=42, average $\frac{42}{3}=14$) than the top cube (sum: 8+10+12=30, average $\frac{30}{3}=10$), so the bottom cube is hotter. When two objects touch, thermal energy (kinetic energy of molecules) transfers from the hotter object to the cooler one until they reach thermal equilibrium (same temperature, which is between the two starting temperatures). Option a is wrong because molecules won't all have exactly 14 energy (average will balance, not each molecule). Option c is wrong because the bottom cube is hotter, not cooler. Option d is wrong because "cold energy" doesn't exist; only thermal energy transfers from hot to cold.

Answer:

b. Before the cubes touch, the bottom cube is hotter than the top cube. Once the cubes are touching, the bottom cube will transfer kinetic energy to the molecules in the cooler top cube until both cubes reach the same temperature, which will be in between their starting temperatures.