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T - (T: Temperature in degrees Kelvin, Te: Temperature in degrees Celsius)
[tex]\[\Delta U = Q - W\][/tex]
([tex]\(\Delta U\)[/tex]: Change in a system's internal energy, Q: Energy transferred to or from system as heat, W: Energy transferred to or from system as work)
[tex]\[\text{eff} = \frac{W_{\text{net}}}{Q_h}\][/tex]
([tex]\(\text{eff}\)[/tex]: Efficiency of a heat engine, [tex]\(W_{\text{net}}\)[/tex]: Work done by the heat engine, [tex]\(Q_h\)[/tex]: Energy added to the system as heat during one cycle)

1. The freezing point of seawater at sea level is 270.6 K. Using the equation below, find the freezing point of seawater in degrees Celsius.
A. 2.55°C
B. -2.55°C
C. 543.75°C
D. -543.75°C

2. What must be true about two given objects for energy to be transferred as heat between them?
A. The objects must be large.
B. The objects must be hot.
C. The objects must contain a large amount of energy.
D. The objects must have different temperatures.

3. A metal spoon is placed in one of two identical cups of coffee. After a few minutes, the cup with the spoon has a lower temperature than the cup without the spoon. Which statement best explains this?
A. Energy is removed from the coffee mostly by conduction through the spoon.
B. Energy is removed from the coffee mostly by convection through the spoon.
C. Energy is removed from the coffee mostly by radiation through the spoon.
D. There is no energy transfer between the spoon and the coffee.

Sagot :

GinnyAnswer
Certainly! Let's tackle each question step by step for a clear solution.

### 1. Finding the Freezing Point of Sea Water in Degrees Celsius

The freezing point of sea water at sea level is given as [tex]\( 270.6 \)[/tex] Kelvin (K). We want to convert this temperature to Celsius (°C) using the equation:

[tex]\[ T(K) = T(°C) + 273.15 \][/tex]

Rearranging the formula to solve for [tex]\( T(°C) \)[/tex], we have:

[tex]\[ T(°C) = T(K) - 273.15 \][/tex]

Plugging in the given value:

[tex]\[ T(°C) = 270.6 - 273.15 = -2.55 \][/tex]

Hence, the freezing point of sea water in degrees Celsius is [tex]\(-2.55°C\)[/tex]. Therefore, the correct answer is:

B. -2.55°C

### 2. Conditions for Energy Transfer as Heat Between Two Objects

For energy to be transferred as heat between two objects, they must have different temperatures. Heat naturally flows from the object at a higher temperature to the object at a lower temperature until thermal equilibrium is reached.

Therefore, the correct condition that must be true is:

D. The objects must have different temperatures.

### 3. Explanation for the Temperature Difference in Coffee Cups

When a metal spoon is placed in a cup of coffee, the phenomenon of conduction comes into play. Metal is a good conductor of heat, meaning it can transfer thermal energy efficiently. As the metal spoon absorbs heat from the hot coffee, it conducts the heat away from the coffee and eventually dissipates it into the surrounding air or its own cooler parts.

This results in the cup of coffee with the spoon having a lower temperature compared to the cup without the spoon because heat is being transferred from the coffee to the spoon.

Thus, the best explanation for this observation is:

A. Energy is removed from the coffee mostly by conduction through the spoon.

To summarize:

1. B. -2.55°C
2. D. The objects must have different temperatures.
3. A. Energy is removed from the coffee mostly by conduction through the spoon.
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