题型概述：运动与力Question types: kinematics & forces
本组用 2024–2025 年真题练习五种模型：射程比例、静力平衡、相对运动、运动计时和力的分解。Part I 要快速排除干扰项；Part II 要说明建模假设并写出推导。常见失误是漏算往返时间、把路程当位移，以及把力的大小直接当作沿斜面分量。These 2024–2025 questions cover range scaling, equilibrium, relative motion, timing and force resolution. Part I rewards eliminating distractors; Part II requires assumptions and a derivation. Common errors are missing the return time, confusing distance with displacement, and using a force magnitude instead of its component.
计分说明：所提供源文件未标注官方分值。本页每个可判分答案计 1 个练习分，总计 6 练习分；不是官方试卷分值。符号推导以明确标注的数值检验练习。Scoring: the supplied sources omit official marks. Each graded response earns one practice point, for 6 practice points total; these are not official paper marks. Symbolic results use explicitly labelled numerical checks.
1先定模型，再选公式Choose the model first
匀加速公式要求加速度恒定。斜抛时应把水平和竖直方向分开，两个方向共用同一时间。Constant-acceleration equations require constant acceleration. For projectiles, separate horizontal and vertical motion while sharing the same time.
自由落体取 a = −g；本文数值统一用 g = 9.81 m/s²。For upward-positive free fall use a = −g; numerical examples use g = 9.81 m/s².
2画对作用在物体上的力Identify forces on the chosen body
物体静止时，任意方向的合力都为零。支持力垂直接触面，重力竖直向下；先定方向再分解。For a stationary body, the net force is zero in every direction. The normal force is perpendicular to contact and weight is vertically down; determine directions before resolving.
选择沿斜面和垂直斜面坐标往往最省步骤。Axes parallel and normal to a slope usually simplify the equations.
3用共同时间连接运动Connect motions through shared time
路程是速率对时间的累积。相向运动的间距由两物体共同缩小，不要漏掉其中一个的贡献。Distance accumulates speed over time. Both approaching objects reduce their separation; include both contributions.
下方小实验固定合力 10 N，查看质量怎样改变加速度。The small experiment below fixes net force at 10 N and varies mass.
| 子题型Subtype | 识别特征Recognise | 核心步骤Key step | 真题Question |
|---|---|---|---|
| 射程的平方关系Range scales as speed squared | 同角度、倍速Same angle, doubled speed | 飞行时间 × 水平速度Flight time × horizontal speed | 2025 I-4 |
| 水位不变的弹簧A spring keeping the level fixed | 水面距地不变Fixed surface height | 高度变化与力平衡Height change and balance | 2025 I-6 |
| 相向运动的共同计时One clock for closing walls | 两边界相向移动Closing boundaries | 先求总时间Find total time first | 2024 I-8 |
| 用抛书测量时间Timing a journey with a book | 反复抛接、计次数Repeated throws and count | 完整周期 × 次数Full cycle × count | 2025 II-7 |
| 两种支撑力Two ways to support a block | 同一物块、两种支撑Same block, two supports | 沿斜面分解后消元Resolve then eliminate | 2024 II-15 |