📚 Engineering Admissions Assessment 2018 Section 2 Answer Key | 工程入学评估 2018 第二部分答案关键
The Engineering Admissions Assessment (EAA) 2018 Section 2 is designed to stretch strong A-level candidates with multi-step physics and applied mathematics. This article explains how to use the official answer key, what the marking scheme rewards, and how to analyse the most common question types.
工程入学评估 2018 第二部分旨在用多步骤物理和应用数学题考查优秀 A-level 学生。本文将说明如何使用官方答案关键、评分方案奖励什么，以及如何分析最常见题型。
1. Overview of the 2018 EAA Section 2 | 2018年 EAA 第二部分概述
Section 2 of the 2018 EAA contained 20 multiple-choice questions, each with five options. The questions were designed to test advanced physics and mathematical reasoning beyond standard A-level recall.
2018年 EAA 第二部分包含20道选择题，每题五个选项。题目旨在考查超出标准 A-level 记忆的高级物理和数学推理。
The answer key is a simple letter grid, but its value comes from using it alongside the mark scheme to identify exactly where marks are earned or lost. The paper is time-pressured, so candidates must move quickly through calculation-heavy items.
答案关键虽然只是字母表，但它的价值在于结合评分方案使用，以准确找出得分点和失分点。试卷时间紧张，考生必须快速完成计算量大的题目。
2. What the Official Answer Key Shows | 官方答案关键显示什么
The official answer key usually lists the correct option for each question and may include a brief indication of the topic tested. For example, a question on projectile motion might be tagged as ‘Mechanics – kinematics’.
官方答案关键通常列出每道题的正确选项，并可能简要标明所考主题。例如，一道关于抛体运动的问题会标注为“力学 – 运动学”。
You should never treat the answer key as a shortcut to memorising letters. Instead, use it to classify your errors: did you misread the question, apply the wrong model, or make an algebra slip?
绝不应把答案关键当作记忆字母的捷径。相反，要用它给错误分类：是读题不清、模型用错，还是代数失误？
3. How Section 2 Is Scored | 第二部分如何评分
In 2018, each correct answer in Section 2 was worth one raw mark. There was no negative marking, so guessing was not penalised, but the test was designed so that random guessing rarely produced a competitive score.
2018年，第二部分每道正确题得1原始分。没有倒扣分，因此猜测不会受罚，但考试设计使随机猜测很难获得有竞争力的分数。
Scores from Section 2 were combined with Section 1 to form an overall EAA result, and Cambridge used this alongside interview and other data to decide which candidates to call for interview.
第二部分的分数与第一部分合并得出 EAA 总分，剑桥将其与面试及其他数据一起使用，决定哪些申请者进入面试。
4. Using the Answer Key for Review | 利用答案关键进行复习
When you finish a timed 2018 Section 2 paper, first mark your answers against the key. For every wrong answer, write down the letter you chose and the letter shown in the key, then explain in one sentence why you think the correct answer is correct.
限时完成2018年第二部分后，首先根据答案关键评分。对每道错题，写下你选的字母和答案关键中的字母，然后用一句话解释你认为正确答案为什么正确。
Only after this self-explanation should you consult the detailed model solutions. This prevents you from developing a false sense of mastery from simply reading the solution.
只有在完成自我解释之后，才查阅详细模型答案。这样可以避免仅通过阅读答案而产生虚假的掌握感。
5. Key Topic 1: Mechanics and Energy | 关键主题1：力学与能量
The most heavily weighted topics in the 2018 Section 2 were mechanics, electricity, materials, and applied mathematics. Questions often combined two areas, such as energy conservation with circular motion or circuit analysis with power dissipation.
2018年第二部分权重最大的主题是力学、电学、材料和应用数学。题目经常结合两个领域，例如能量守恒与圆周运动，或电路分析与功率耗散。
A typical mechanics question asked candidates to find the minimum speed for complete vertical circular motion, while a typical electricity question involved calculating the potential difference across a component in a network.
典型的力学题要求考生求出完成竖直圆周运动的最低速度，而典型的电学题涉及计算网络中元件两端的电势差。
6. Worked Example: Circular Motion | 例题：圆周运动
Consider a ball of mass 0.5 kg moving in a vertical circle of radius 1.2 m. To find the minimum speed at the top, set the centripetal force equal to the weight at the top:
考虑一个质量为0.5 kg的小球在半径1.2 m的竖直圆周上运动。要求顶端的最小速度，令顶端向心力等于重力：
mg = mv² ÷ r → v = √(gr)
With g = 9.8 m s⁻² and r = 1.2 m, this gives v ≈ √(9.8 × 1.2) ≈ 3.43 m s⁻¹. The 2018 answer key would show the option closest to 3.4 m s⁻¹.
取 g = 9.8 m s⁻²、r = 1.2 m，得到 v ≈ √(9.8 × 1.2) ≈ 3.43 m s⁻¹。2018答案关键会显示最接近3.4 m s⁻¹的选项。
The most common error in this question type is forgetting that at the top the normal contact force can go to zero, so tension or reaction does not contribute to the centripetal force.
这类问题最常见的错误是忘记在顶端法向接触力可为零，因此绳子张力或支持力不提供向心力。
7. Key Topic 2: Electricity and Circuits | 关键主题2：电学与电路
Circuit questions in 2018 frequently asked candidates to combine resistors in series and parallel, then use Ohm’s law and the power formula P = V² ÷ R or P = I²R.
2018年电路题经常要求考生组合串联和并联电阻，然后使用欧姆定律及功率公式 P = V² ÷ R 或 P = I²R。
A common setup was a battery of negligible internal resistance connected to a network of three resistors. The key tested whether you could identify which resistors were in parallel and which were in series.
常见的设置是一个内阻可忽略的电池连接三个电阻网络。答案关键考查你能否判断哪些电阻并联、哪些串联。
8. Worked Example: Circuit Analysis | 例题：电路分析
Worked example: a 12 V battery is connected to a 6 Ω resistor in series with a parallel combination of 3 Ω and 6 Ω. First find the parallel equivalent:
例题：一个12 V电池连接一个6 Ω电阻，该电阻与3 Ω和6 Ω的并联组合串联。先求并联等效电阻：
1 ÷ Rₚ = 1 ÷ 3 + 1 ÷ 6 = 1 ÷ 2 → Rₚ = 2 Ω
The total resistance is then 6 Ω + 2 Ω = 8 Ω, so the main current is 12 V ÷ 8 Ω = 1.5 A. The potential difference across the 6 Ω resistor is 1.5 A × 6 Ω = 9 V.
总电阻为 6 Ω + 2 Ω = 8 Ω，因此主电流为 12 V ÷ 8 Ω = 1.5 A。6 Ω电阻两端的电势差为 1.5 A × 6 Ω = 9 V。
The remaining 3 V appears across the parallel pair, so the current in the 3 Ω resistor is 3 V ÷ 3 Ω = 1 A. The correct option in the 2018 key would be the one matching this current.
剩余3 V加在并联组合上，因此通过3 Ω电阻的电流为 3 V ÷ 3 Ω = 1 A。2018答案关键中正确选项会与这个电流匹配。
9. Key Topic 3: Materials and Deformation | 关键主题3：材料与形变
Materials questions in 2018 Section 2 often involved stress, strain, the Young modulus, and elastic strain energy. A typical task was to find the energy stored in a stretched wire or spring.
2018年第二部分的材料题常涉及应力、应变、杨氏模量和弹性应变能。典型任务是求拉伸金属丝或弹簧中储存的能量。
The formula for elastic strain energy per unit volume is ½ × stress × strain, and for a spring the stored energy is ½ kx². The answer key rewarded correct unit conversion as much as the final numerical value.
单位体积弹性应变能公式为 ½ × 应力 × 应变，弹簧储存能量为 ½ kx²。答案关键对单位转换和最终数值同样给分。
10. Common Errors and How the Key Helps | 常见错误及答案关键如何帮助
When reviewing the 2018 key, watch for three recurring errors: using the gravitational potential energy formula mgh in a non-uniform field, adding resistors incorrectly as if all were in series, and confusing the direction of induced current in Lenz’s law questions.
复习2018答案关键时要留意三个常见错误：在非均匀场中错误使用重力势能公式 mgh；把所有电阻误当作串联相加；在楞次定律问题中混淆感应电流方向。
The key can help you spot these because the wrong options are usually not random; they are derived from exactly these common errors. If you chose a wrong letter, you can often reconstruct the mistake the examiner expected you to make.
答案关键能帮助你发现这些问题，因为错误选项通常并非随机，而是来自这些常见错误。如果你选
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