Question

In order to fit a metal rim to the wooden wheel of a bullock cart, the metal rim is ______________________________________ and placed on the wooden wheel and ______________________________________. This process works because ______________________________________.

• A. Heated, cooled, the metal expands as it cools
• B. Cooled, heated, the metal shrinks as it cools
• C. Heated, cooled, the metal shrinks as it cools
• D. Cooled, heated, the metal expands as it cools

Hint:

Remember the basic principle of thermal physics: Heat causes expansion, and cooling causes contraction. This is a fundamental concept often applied in engineering and everyday phenomena.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This question is about the practical application of thermal expansion and contraction of solids. Most materials, especially metals, expand when heated and contract when cooled. This principle is used by blacksmiths to fit metal parts tightly.
Step 2: Detailed Explanation:


First Action: To fit a metal rim onto a wooden wheel, the rim is intentionally made with a slightly smaller inner diameter than the outer diameter of the wheel. To make it fit, the rim's diameter must be increased. This is achieved by uniformly heating the metal rim. Heating causes the metal to expand. So, the first blank is Heated.
Second Action: While the rim is expanded due to the heat, it is quickly placed over the wooden wheel. As the rim cools down to room temperature, it starts to contract or shrink. So, the second blank is cooled.
The Principle: The reason this process creates a very tight fit is that as the metal rim cools, it attempts to return to its original smaller size, exerting a large compressive force on the wooden wheel. This phenomenon is called thermal contraction. The statement that explains why this works is the metal shrinks as it cools.
Combining these parts, the full statement is: "the metal rim is Heated and placed on the wooden wheel and cooled. This process works because the metal shrinks as it cools". This matches option (C).

Answer 2

Thermal expansion tells us that heating a solid makes it expand and cooling it makes it shrink back, so checking each option against this one rule quickly rules out three of the four choices.

1. Heated, cooled, the metal expands as it cools: the first two blanks are right, since heating before fitting and cooling afterwards is exactly what blacksmiths do, but the last part is backwards, cooling a metal makes it contract, not expand, so this option is wrong.
2. Cooled, heated, the metal shrinks as it cools: cooling the rim first would shrink it further, making it even harder to fit over the wheel, and reheating it afterwards would make it expand again and loosen the fit, so the order here is the opposite of what is needed.
3. Heated, cooled, the metal shrinks as it cools: heating expands the rim enough to slide over the wheel, and as it cools afterward it shrinks back down, clamping tightly onto the wood; this matches both the correct sequence of actions and the correct physical reason.
4. Cooled, heated, the metal expands as it cools: cooling the rim before fitting would shrink it rather than help it fit over the wheel, and the final clause describing expansion on cooling is also physically backwards.

Only the option that starts with heating, ends with cooling, and correctly states that cooling shrinks the metal matches how this fitting method actually works.

Therefore, the correct answer is Heated, cooled, the metal shrinks as it cools.