【People's Education Press】High School Physics: Compulsory Course 1: The Mystery of Speed in the Evolution of Transportation from Chariots to C919

From the Harappan chariot of the Indus Valley around 2000 BC,Harappan chariot, to today's Shanghai Maglev traveling at a top speed of 430 km/h,Shanghai Maglevhuman civilization's leap is not just about increased speed, but also about the evolution of how we describe motion. To quantitatively analyze this transformation, we must master two core physical models.

1. Physical Concept:Point Mass

When studying the global flight path of a C919 aircraft or the 33-kilometer route of a maglev train, its large size is negligible compared to the scale of the path. At this point, we can ignore the object's shape and size, simplifying it to a mass-bearing 'point'.Note: A point mass is a relative concept. If analyzing the nose attitude during an aircraft's landing, it cannot be treated as a point mass.

2. Physical Concept:Reference Frame

Motion is relative. When the Shanghai Maglev travels at 430 km/h, if passengers inside the cabin are used as the reference frame, the train appears stationary; if the ground track is used, it appears to be moving at extreme speed. Before quantitatively describing motion, a reference frame must be selected in advance.

The Evolutionary View of Speed

From the slow, random motion of chariots to the 10,000-meter uniform cruise of the C919, physics centers on transforming complex position-time changes ($x-t$) into precise functional relationships. All high-speed transportation fundamentally represents ultimate mastery over the patterns of motion parameters.

QUESTION 1

In the 'tape-cutting method' experiment to study the motion of a cart (as shown in Figure 2.1-4), if paper strips cut every 0.1 seconds are placed side by side on a coordinate system, what does the line connecting the tops of these strips represent?

The displacement magnitude of the cart at each moment

The trend of the cart’s speed changing over time (prototype of a v-t graph)

The variation in the vibration frequency of the ticker timer

The magnitude of the traction force acting on the cart

QUESTION 2

The train's initial speed is $36 \text{ km/h}$, with an acceleration of $0.2 \text{ m/s}^2$ on a downhill slope. The final speed reaches $54 \text{ km/h}$. Find the time it takes for the train to travel this section.

90 s

25 s

15 s

5 s

QUESTION 3

Which of the following statements about the 'point mass' is correct?

Any object with small volume can always be considered a point mass

When studying the C919’s flight trajectory in the atmosphere, it can be treated as a point mass

A point mass is a real, special object

When studying the time it takes for a maglev train to pass a certain utility pole, it can be treated as a point mass

QUESTION 4

Two cars are driving side by side in the same direction at constant speed on a highway. If one car is used as the reference frame, the other car is:

in motion

stationary

first in motion, then stationary

QUESTION 5

The total length of the Shanghai Maglev line is 33 km, with a full journey taking approximately 7.5 minutes. If it travels at a constant speed of 430 km/h for 30 seconds, what is the approximate displacement during this period?

3.58 km

12.9 km

33 km