Question

a very hot mug of coffee is near a large unheated swimming pool holding 2.0 × 10⁶kg of water. which statement is correct?
○ a. the internal energy of a substance depends only on its temperature.
○ b. when the temperature of the mug of coffee falls, its internal energy will decrease.
○ c. if the mug of coffee is tipped in the pool, the coffee will lose much more internal energy than the water in the pool gains.
○ d. the internal energy of the water in the pool is lower than the internal energy of the mug of coffee.

Explanation:

• Option A: Internal energy depends on temperature, mass, and state. So this option is wrong.
• Option B: Internal energy is related to temperature. When temperature falls (for a given mass and state), internal energy decreases. This is correct.
• Option C: According to the law of conservation of energy, the coffee loses internal energy equal to what the water gains (assuming no heat loss to surroundings). So this option is wrong.
• Option D: The pool has a huge mass. Even if coffee is hot, due to the large mass of pool water, its internal energy (which is a function of mass, temperature etc.) is likely higher. So this option is wrong.

Answer:

B. When the temperature of the mug of coffee falls, its internal energy will decrease.