📚 Year 7 CIE Engineering: Mock Unit Test Walkthrough | CIE 7年级工程：单元测试模拟卷解析
This article provides a detailed walkthrough of a Year 7 CIE Engineering mock unit test. Each question is broken down with clear explanations, common misconceptions, and key points to help you revise effectively. By working through these questions, you will strengthen your understanding of structures, mechanisms, materials, the design process, and safety in engineering.
本文详细解析了一份CIE 7年级工程单元测试模拟卷。每道题目都有清晰的解释、常见错误和关键要点，以帮助您有效复习。通过完成这些题目，您将加深对工程中结构、机构、材料、设计流程和安全等知识的理解。
1. Forces in a Loaded Beam | 承载梁中的力
Question: A beam bridge supports a weight at its centre. Which stress acts on the top surface of the beam?
A. Tension
B. Compression
C. Shear
D. Torsion
题目：一座梁桥在中心承受重量。梁的上表面受到哪种应力？
A. 拉伸
B. 压缩
C. 剪切
D. 扭转
Answer: B. Compression. When a simply supported beam bends downwards under a central load, the top fibres are pushed together, experiencing compressive stress. The bottom fibres are stretched under tension. The neutral axis in the middle experiences no stress.
答案：B. 压缩。当简支梁在中心载荷下向下弯曲时，顶部纤维被挤压，承受压应力。底部纤维被拉伸，承受拉应力。中间的轴无应力。
Common mistake: Students often confuse tension and compression. Remember: 'top compressed, bottom stretched' for a beam loaded in the middle. This helps when analysing bridges and floor joists.
常见错误：学生经常混淆拉伸和压缩。记住：对于中部受载的梁，“顶部受压，底部受拉”。这在分析桥梁和楼板搁栅时很有用。
2. Material Selection for a Bridge | 桥梁的材料选择
Question: Why is steel commonly used for the main girders of a large bridge instead of pure aluminium?
题目：为什么大型桥梁的主梁通常使用钢材，而不使用纯铝？
Answer: Steel has a much higher strength and stiffness than pure aluminium, meaning it can carry heavier loads without bending too much. It is also tougher and more durable, resisting fatigue cracks over many years of traffic. While aluminium is lighter, its lower elastic modulus and yield strength would require much thicker sections, making the design impractical for long spans.
答案：钢材的强度和刚度远高于纯铝，这意味着它能承受更重的载荷而不会过度弯曲。钢材还具有更好的韧性和耐久性，能抵抗多年交通引起的疲劳裂纹。虽然铝更轻，但其较低的弹性模量和屈服强度需要更厚的截面，这使得其用于大跨度不切实际。
Key takeaway: Engineers choose materials by balancing strength, stiffness, weight, cost, and workability. For structural elements where stiffness is critical, steel is preferred over aluminium.
关键要点：工程师通过平衡强度、刚度、重量、成本和可加工性来选择材料。对于刚度至关重要的结构元件，钢材优于铝材。
3. Class 1 Lever and Its Examples | 一类杠杆及其例子
Question: A crowbar is used to lift a heavy object. Where is the fulcrum, effort, and load positioned in this lever system?
题目：用撬棍抬起重物。在这个杠杆系统中，支点、用力点和负载点的位置如何？
Answer: This is a Class 1 lever. The fulcrum is placed between the effort and the load. In a crowbar, the end that pivots against the ground is the fulcrum, the downward push by the user is the effort, and the heavy object being lifted is the load on the other side. Scissors and see-saws are also Class 1 levers.
答案：这是一类杠杆。支点位于用力点和负载之间。在撬棍中，与地面接触的端部是支点，用户向下推的是用力点，被抬起另一端的重物是负载点。剪刀和跷跷板也是一类杠杆的例子。
Memory aid: In a Class 1 lever, 'F' (fulcrum) is always in the middle. Always identify the pivot first.
记忆方法：在一类杠杆中，“F”（支点）总是在中间。务必先找到旋转点。
4. Mechanical Advantage of a Lever | 杠杆的机械效益
Question: A Class 1 lever has an effort arm of 60 cm and a load arm of 15 cm. Calculate the mechanical advantage (MA) and explain what it tells you.
题目：一个一类杠杆的用力臂长度为60 cm，负载臂长度为15 cm。计算机械效益（MA）并解释其含义。
Answer: The mechanical advantage of a lever is given by the ratio of the effort arm length to the load arm length. MA = Effort arm ÷ Load arm = 60 cm ÷ 15 cm = 4. This means the lever multiplies the input force by 4; you can lift a load four times heavier than the effort you apply, but the effort must move a greater distance.
答案：杠杆的机械效益由用力臂长度与负载臂长度的比值给出。MA = 用力臂 ÷ 负载臂 = 60 cm ÷ 15 cm = 4。这意味着杠杆将输入力放大了4倍；您可以抬起比您施加的力重四倍的负载，但用力点必须移动更大的距离。
Common error: Always divide effort arm by load arm, not the other way around. Write the formula clearly before substituting numbers.
常见错误：始终是用全力臂除以负载臂，而不是反过来。代入数字前先清楚地写出公式。
5. Pulley Systems and Load Sharing | 滑轮系统与负载分配
Question: A simple pulley system consists of two pulleys with a rope looped around them. The effort is pulled downwards, and the load is attached to the moving pulley. How does this system provide mechanical advantage?
题目：一个简单的滑轮系统由两个滑轮组成，绳索绕过它们。用力向下拉，负载挂在动滑轮上。这个系统如何提供机械效益？
Answer: In this arrangement, the load is supported by two rope segments, so the tension in each rope is half the load weight. The effort needed is approximately half the load, giving an MA of about 2. The fixed pulley only changes the direction of the force; the moving pulley is what multiplies the force.
答案：在这种布置中，负载由两段绳索支撑，因此每段绳索的张力是负载重量的一半。所需的用力大约是负载的一半，因此MA约为2。定滑轮只改变力的方向；动滑轮才是放大力的元件。
Sketch tip: When analysing pulleys, count the number of rope strands that support the moving pulley block. This number directly equals the ideal MA, ignoring friction.
绘制技巧：分析滑轮时，数一下支撑动滑轮组的绳段数。忽略摩擦时，这个数字直接等于理想MA。
6. Types of Motion in Mechanisms | 机构中的运动类型
Question: A crank and slider mechanism converts one type of motion into another. Identify the input and output motions.
题目：曲柄滑块机构将一种运动转换为另一种。指出输入和输出运动。
Answer: The input is rotary motion from a rotating crank. The output is reciprocating (back-and-forth linear) motion of the slider. This is found in internal combustion engines where the piston moves linearly. The opposite conversion (linear to rotary) occurs in a crank-driven pump. Other motion types include oscillating (swinging) and intermittent motion.
答案：输入是来自旋转曲柄的旋转运动。输出是滑块的往复（直线来回）运动。这在内燃机中可见，活塞进行直线运动。相反转换（直线变为旋转）发生在曲柄驱动的泵中。其他运动类型包括摆动和间歇运动。
Quick check: Know the four basic types: linear, rotary, reciprocating, and oscillating. Be able to match them to real-world mechanisms.
快速检查：了解四种基本类型：直线、旋转、往复和摆动。要能将它们与实际机构匹配。
7. Gear Train Speed Calculation | 齿轮系转速计算
Question: A driving gear with 20 teeth rotates at 100 rpm. It meshes with a driven gear of 50 teeth. Calculate the speed of the driven gear and determine whether it is a speeding-up or slowing-down system.
题目：一个20齿的主动齿轮以100 rpm旋转。它与一个50齿的从动齿轮啮合。计算从动齿轮的转速，并判断该系统是加速还是减速。
Answer: Use the gear ratio formula: eed = (Driver teeth ÷ Driven teeth) × Driver speed = (20 ÷ 50) × 100 = 0.4 × 100 = 40 rpm. The driven gear turns more slowly than the driver, so it is a reducing (torque-increasing) system. The speed ratio is 1 : 0.4.
答案：使用齿轮比公式：从动齿轮转速 = (主动齿轮齿数 ÷ 从动齿轮齿数) × 主动齿轮转速 = (20 ÷ 50) × 100 = 0.4 × 100 = 40 rpm。从动齿轮转得比主动齿轮慢，因此这是一个减速（增矩）系统。转速比为1 : 0.4。
Remember: A smaller driver turning a larger driven gear reduces speed but increases torque. Use the correct order in the division.
牢记：小主动齿轮带动大从动齿轮会降低转速但增加扭矩。除法中使用正确的顺序。
8. The Design Cycle in Engineering | 工程设计循环
Question: After building a prototype, an engineer tests it and finds that it breaks under a load of 50 N. According to the design cycle, what should the engineer do next?
题目：工程师在制作原型后对其进行测试，发现它在50 N的载荷下断裂。根据设计循环，工程师接下来应该做什么？
Answer: st : The engineer should evaluate the test results and then go back to modify the design or choose stronger materials. This is the 'evaluate and redesign' luate → redesign. Testing often reveals flaws that require looping back to earlier stages.
答案：工程师应评估测试结果，然后返回修改设计或选择更坚固的材料。这是“评估与重新设计”的步骤。设计循环是迭代的：确定问题 → 研究 → 设计 → 建造 → 测试 → 评估 → 重新设计。测试通常会揭示缺陷，需要回到前面的阶段。
Exam tip: Never skip evaluation. It is the evidence that leads to improvements. Explain how you would change the design based on specific test data.
考试技巧：永远不要跳过评估环节。它是导致改进的依据。解释如何根据具体的测试数据更改设计。
9. Workshop Safety Essentials | 车间安全要点
Question: List three essential safety rules when using a hand saw in the engineering workshop.
题目：列出在工程车间使用手锯时的三条基本安全规则。
Answer: 1. Always secure the workpiece in a vice before cutting; never hold it by hand. 2. Wear safety goggles to protect your eyes from swarf and broken blade teeth. 3. Check the blade for sharpness and correct tension; a dull or loose blade can snap. Also, tie back long hair and remove dangling jewellery.
答案：1. 切割前务必将工件夹在台虎钳上；切勿用手把持。2. 佩戴防护眼镜，保护眼睛免受切屑和断齿的伤害。3. 检查锯条的锋利度和正确的松紧；钝的或松弛的锯条可能断裂。此外，要扎起长头发并摘掉悬垂的首饰。
Why it matters: Most workshop accidents are caused by poor preparation or rushing. Develop safe habits from Year 7 onwards.
重要性：大多数车间事故是由准备不充分或仓促行事造成的。从7年级开始养成良好的安全习惯。
10. Orthographic Projection and Dimensioning | 正交投影与尺寸标注
Question: A drawing shows the front view and plan view of a simple L-shaped bracket. What information does the side view add, and why are dimensions placed outside the views?
题目：一幅图纸展示了一个简单L形支架的主视图和俯视图。侧视图增加了什么信息？为什么尺寸标注要放在视图之外？
Answer: The side view reveals the depth or thickness not fully visible in the front and plan views. For an L-shape, it shows the height of the vertical arm and the depth of the base. Dimensions are placed outside views to keep the drawing clear and avoid clutter, following BS 8888 conventions. Extension lines lead from the feature to the dimension line.
答案：侧视图揭示了在主视图和俯视图中无法完全看到的深度或厚度。对于L形件，它显示了垂直臂的高度和底座的深度。尺寸标注放在视图外是为了保持图纸清晰、避免混乱，符合BS 8888标准。尺寸界线从特征引向尺寸线。
Exam expectation: Be able to identify the three standard views (front, side, plan) and add simple dimensions in the correct positions. Always use millimetres unless specified.
考试期望：能够识别三个标准视图（主视图、侧视图、俯视图），并在正确位置添加简单的尺寸。除非另有规定，始终使用毫米。
Published by TutorHao | Engineering Revision Series | aleveler.com
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