📚 Distance-Time Graph Exam Question and Mark Scheme | 距离-时间图考试真题与评分标准
Distance-time graphs are one of the most common types of questions in the CIE KS3 Science Checkpoint. They test your ability to read a graph, describe motion, and calculate speed. This article breaks down an exam-style question and its mark scheme, so you can see exactly what examiners expect.
距离-时间图是 CIE KS3 科学 Checkpoint 中最常见的题型之一。它考查你看图、描述运动和计算速度的能力。本文拆解一道考试风格真题及其评分标准，让你清楚了解考官的评分要求。
1. What is a Distance-Time Graph? | 什么是距离-时间图？
A distance-time graph shows how the distance travelled by an object changes over time. Time is always plotted on the horizontal x-axis, and distance is always plotted on the vertical y-axis.
距离-时间图显示物体运动距离随时间变化的情况。时间总是画在水平 x 轴上，距离总是画在竖直 y 轴上。
In CIE KS3 exams, you may be given a table of results and asked to plot the points, or you may be given a ready-drawn graph and asked to describe or calculate from it.
在 CIE KS3 考试中，你可能会拿到一张结果表并要求描点，也可能会拿到一张已经画好的图，要求你根据图进行描述或计算。
The main features of a distance-time graph are the labels, units, points, and the shape of the line. Examiners check each of these carefully.
距离-时间图的主要要素包括坐标轴标签、单位、数据点和图线形状。考官会仔细检查每一项。
2. Reading the Graph: Gradient and Speed | 读图：斜率与速度
The gradient of a distance-time graph tells you the speed of the object. A steeper gradient means a higher speed, while a flatter gradient means a lower speed.
距离-时间图的斜率表示物体的速度。斜率越陡，速度越大；斜率越平缓，速度越小。
A straight horizontal line means the object is stationary. The distance is not increasing, so the speed is zero.
一条水平的直线表示物体静止不动。距离没有增加，因此速度为零。
To calculate speed from a distance-time graph, use the equation below. Always include the correct unit, such as m/s or km/h.
要从距离-时间图计算速度，请使用下面的公式。务必写出正确单位，如 m/s 或 km/h。
speed = distance ÷ time
速度 = 距离 ÷ 时间
3. Common Misconceptions | 常见误区
Many students think that a steep line on a distance-time graph means the object is accelerating. In fact, a straight steep line means a constant high speed.
许多学生认为距离-时间图上一条陡峭的线表示物体在加速。实际上，一条陡峭的直线表示物体以较高的恒定速度运动。
Another common error is confusing distance travelled with displacement. In KS3 distance-time graphs, you always use the total distance along the path, not just the final position.
另一个常见错误是混淆运动距离和位移。在 KS3 的距离-时间图中，你总是使用沿路径的总距离，而不仅仅是最终位置。
Students also forget to label the axes with units. If the axes are labelled 'Time' and 'Distance' without 's' and 'm', a mark may be lost.
学生还会忘记给坐标轴标注单位。如果坐标轴只写了 'Time' 和 'Distance' 而没有写 's' 和 'm'，可能会丢分。
4. Exam-Style Question: Cyclist | 考试真题：骑车人
Here is a typical CIE KS3 distance-time graph question. Read it carefully before looking at the mark scheme.
以下是一道典型的 CIE KS3 距离-时间图题目。在看评分标准之前，请先仔细读题。
Question (Total 6 marks)
A cyclist travels along a straight road. The table shows the distance she travels over 10 seconds.
一名骑车人沿笔直道路骑行。下表显示她在 10 秒内行驶的距离。
| Time / s | 0 | 2 | 4 | 6 | 8 | 10 |
|---|---|---|---|---|---|---|
| Distance / m | 0 | 10 | 20 | 30 | 40 | 50 |
(a) Plot the points on the grid and draw a line of best fit. [2 marks]
(a) 在坐标纸上描点并画出最佳拟合线。[2 分]
(b) Describe the motion of the cyclist. [1 mark]
(b) 描述骑车人的运动。[1 分]
(c) Calculate the speed of the cyclist between 0 s and 10 s. Give the unit. [2 marks]
(c) 计算骑车人在 0 秒到 10 秒之间的速度，并写出单位。[2 分]
(d) On the same grid, sketch a line for a second cyclist who travels 40 m in the same time. [1 mark]
(d) 在同一坐标纸上，画出另一位骑车人在相同时间内行驶 40 米的图线。[1 分]
5. Mark Scheme for the Question | 该题的评分标准
The mark scheme below shows how examiners award each mark. You do not need to use exactly the same words, but you must give the same idea.
下面的评分标准显示考官如何给每一分。你不需要使用完全相同的措辞，但必须表达相同的意思。
(a) Plotting and line of best fit [2 marks]
Award 1 mark for all six points plotted correctly within plus or minus half a small square.
6 个点全部画在正确位置，误差在正负半小格以内，得 1 分。
Award 1 mark for a straight line of best fit passing through the origin and all plotted points.
画出一条经过原点和所有描点的直线最佳拟合线，得 1 分。
(b) Describing the motion [1 mark]
Award 1 mark for stating that distance increases at a constant rate, or the cyclist moves at constant speed, or the graph is a straight line through the origin.
答出距离以恒定速率增加，或骑车人做匀速运动，或图线为过原点的直线，得 1 分。
(c) Calculating speed [2 marks]
Award 1 mark for correct substitution: speed = distance ÷ time = 50 ÷ 10.
正确代入公式：速度 = 距离 ÷ 时间 = 50 ÷ 10，得 1 分。
Award 1 mark for the correct answer and unit: 5 m/s.
答案和单位正确：5 m/s，得 1 分。
(d) Sketching the second cyclist [1 mark]
Award 1 mark for a straight line from the origin with a smaller gradient, ending at (10, 40).
从原点出发、斜率较小的直线，终点在 (10, 40)，得 1 分。
6. Worked Solution and Examiner Comments | 详细解答与考官评注
In part (a), the first point is (0, 0) and the last point is (10, 50). Since the points lie in a straight line, your line of best fit should be drawn with a ruler.
在 (a) 部分，第一个点是 (0, 0)，最后一个点是 (10, 50)。由于这些点都在一条直线上，你的最佳拟合线应该用直尺画出。
For part (b), the graph line is straight and passes through the origin, so the cyclist is travelling at a constant speed. Avoid saying 'the cyclist is moving' without explaining how.
对于 (b) 部分，图线是一条过原点的直线，所以骑车人做匀速运动。避免只说 '骑车人在运动' 而不说明运动方式。
In part (c), you must show the formula and the substitution. Writing only '5' without the unit m/s cannot score full marks.
在 (c) 部分，你必须写出公式和代入过程。只写 '5' 而不写单位 m/s 不能得满分。
In part (d), the second cyclist covers 40 m in 10 s, so the speed is 4 m/s. The gradient must be less steep than the first line because 4 m/s is less than 5 m/s.
在 (d) 部分，第二位骑车人在 10 秒内行驶 40 米，因此速度为 4 m/s。因为 4 m/s 小于 5 m/s，所以这条线的斜率必须比第一条线平缓。
7. Second Exam-Style Question: Return Journey | 第二道考试真题：返程运动
Return journeys are very common in CIE KS3 distance-time graph questions. They test whether you can read a graph where the object changes direction.
返程运动是 CIE KS3 距离-时间图题目中非常常见的类型。它考查你是否能读懂物体改变方向的图像。
Question (Total 5 marks)
A runner leaves home and runs 300 m to a shop. She stops at the shop for 60 s, then runs back home in 200 s. The graph below describes her journey.
一名跑步者离开家，跑 300 米到达商店。她在商店停留 60 秒，然后用 200 秒跑回家。下面的图描述了她的行程。
(a) How long did the runner stop at the shop? [1 mark]
(a) 跑步者在商店停留了多长时间？[1 分]
(b) What is the total distance travelled? [1 mark]
(b) 总行驶距离是多少？[1 分]
(c) Calculate the speed of the runner on the return journey. Give the unit. [2 marks]
(c) 计算跑步者返程时的速度，并写出单位。[2 分]
(d) State one difference between the outward journey and the return journey on the graph. [1 mark]
(d) 说出图中去程和返程的一个不同之处。[1 分]
8. Mark Scheme for Return Journey | 返程题评分标准
The mark scheme below shows the key points for each part of the return journey question.
下面的评分标准列出了返程题每个部分的关键给分点。
(a) Stopping time [1 mark]
Award 1 mark for 60 s.
答出 60 s，得 1 分。
(b) Total distance [1 mark]
Award 1 mark for 600 m.
答出 600 m，得 1 分。
he runner travels 300 m to the shop and 300 m back, so total distance = 300 + 300 = 600 m.
跑步者去商店 300 米，回来 300 米，所以总距离 = 300 + 300 = 600 米。
(c) Return speed [2 marks]
Award 1 mark for substitution: speed = 300 ÷ 200.
代入正确：速度 = 300 ÷ 200，得 1 分。
Award 1 mark for correct answer and unit: 1.5 m/s.
答案和单位正确：1.5 m/s，得 1 分。
(d) Difference between outward and return [1 mark]
Award 1 mark for any correct difference, such as the return gradient is less steep, or the return line slopes downwards, or the return speed is smaller.
答出任何正确不同之处，例如返程斜率较平缓，或返程线向下倾斜，或返程速度较小，得 1 分。
9. How to Avoid Losing Marks | 如何避免失分
Examiners report that many marks are lost because students forget to include units, or they do not show the formula when calculating speed.
考官报告显示，很多学生因为忘记写单位，或者在计算速度时没有写出公式而丢分。
Always use a ruler to draw straight lines on a graph. Freehand lines can be inaccurate and may not pass through the points, which can lose marks.
画图上的直线时一定要使用直尺。徒手画线可能不准确，而且可能无法通过所有数据点，从而丢分。
When a question asks you to describe motion, do not just say 'the object moves'. State whether the speed is constant, increasing, or zero, and link your answer to the graph.
当题目要求你描述运动时，不要只说 '物体在运动'。要说明速度是恒定、增大还是为零，并把答案与图像联系起来。
For calculation questions, write the full equation, substitute the numbers, and then write the final answer with a unit. This helps you gain method marks even if the final answer is wrong.
对于计算题，写出完整公式、代入数据，然后写出带单位的最终答案。这样即使最终答案错误，也能得到方法分。
10. Final Summary and Checklist | 最终总结与清单
Before an exam, use this checklist to make sure you are confident with distance-time graphs.
考试前，用这份清单检查你是否已经掌握距离-时间图。
- Time goes on the x-axis, distance goes on the y-axis. / 时间在 x 轴，距离在 y 轴。
- Label both axes with units, such as time / s and distance / m. / 两个坐标轴都要标明单位，如 time / s 和 distance / m。
- A horizontal line means the object is stationary. / 水平线表示物体静止。
- A straight sloping line means constant speed. / 倾斜直线表示匀速运动。
- A steeper gradient means a higher speed. / 斜率越陡，速度越大。
- Use speed = distance ÷ time and include the unit. / 使用速度 = 距离 ÷ 时间，并写出单位。
Practise plotting points from a table and drawing lines of best fit. This skill is tested regularly in CIE KS3 Science papers.
多练习根据表格描点并画出最佳拟合线。这项技能在 CIE KS3 科学试卷中经常考查。
When marking your own work, compare each answer with the mark scheme. Ask yourself: would an examiner give me the mark for this answer?
批改自己的作业时，将每个答案与评分标准对照。问问自己：考官会给我的这个答案分数吗？
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