题型概述：IPC 力学IPC mechanics: question types
IPC 的力学题既有一分选择题，也有五分解释题和多步综合计算题。本模块选取 2023–2025 年的 5 道题，共 24 分。常见失分点是把“相同动量”读成“相同速度”、只写公式不解释受力，以及在功率与能量之间漏掉时间或效率。页面得分是练习反馈；解释题的文字论证仍需对照解答自评。IPC mechanics includes one-mark multiple-choice questions, five-mark explanations and extended calculations. These five questions from 2023–2025 total 24 marks. Common errors include reading equal momentum as equal speed, omitting force reasoning, and losing time or efficiency when converting between power and energy. Page scores are practice feedback; written reasoning still needs self-review against the solution.
1先画受力，再谈运动Start with forces
重力随质量增加，但加速度取决于合力除以质量。阻力的相对影响要看 D/(mg)，而不是只看 D。Weight grows with mass, but acceleration is net force divided by mass. Compare drag through D/(mg), not D alone.
a = ΣF/m；ppressure = F/A = ρgL同一符号 p 有时指压强、有时指动量，先看定义。The symbol p may mean pressure or momentum: check its definition.
2能量账本与功率Energy accounting and power
先选系统，再区分输入能量、有用输出和损耗。功率描述每秒转移多少能量，恒速升降时可用 mgv。Choose the system and separate input, useful output and loss. Power is energy transferred per second; steady lifting or lowering uses mgv.
Eelastic = ½Fx；Eg = mgh；P = E/t；Pout = ηmgvg = 9.8 m/s²；长度用 m，质量用 kg。Use g = 9.8 m/s², lengths in m and masses in kg.
3动量相同，动能未必相同Equal momentum need not mean equal energy
把速度写成 p/m 再代入动能，能直接看出固定动量时的质量关系。下方只改变质量比，观察动能比怎样变化。Replace speed with p/m in kinetic energy to see the mass dependence at fixed momentum. Change the mass ratio below and observe the energy ratio.
p = mv；K = ½mv² = p²/(2m)固定动量：质量越大，速度和动能越小。At fixed momentum, larger mass means lower speed and kinetic energy.
| 子题型Sub-type | 识别特征Clue | 核心步骤Core step | 真题Question |
|---|---|---|---|
| 弹性势能与效率Elastic energy and efficiency | Hooke’s law | 面积 → 效率Area → efficiency | 2025 A2 |
| 压强与密度Pressure and density | same pressure | ρgLρgL | 2024 A3 |
| 动量与动能Momentum and energy | same momentum | p²/(2m)p²/(2m) | 2023 A8 |
| 阻力与落体Drag and falling | same size, different masses | 比较 D/(mg)Compare D/(mg) | 2024 B12 |
| 重力储能Gravity storage | grid, cables | 能量 → 功率 → 拉力Energy → power → tension | 2023 C13 |