Analysis: The abscissa is time t and the ordinate is distance s, so the slope of the curve is the rate s/t = v. Therefore, it can be seen that the slope is 2/2= 1 at first, then becomes 0, and finally (6-2)÷(7-5)=2, and the unit is m/s. So the three conclusions are,

Answer: 1. When the time is 0-2s, the car moves in a straight line at a constant speed of 1m/s ... 2. When the time is 2-5s, the car is stationary. 3. When the time is 5-7 seconds, the car moves in a straight line at a constant speed of 2m/s. ..

10、

Analysis: When the locomotive just entered the railway bridge, we thought that the train began to enter the railway bridge; When the train has just left the iron bridge, it needs to walk the length of another train, that is, when the tail of the train also leaves the iron bridge, we think that the train has left the iron bridge. So the distance traveled by the train is the length of the iron bridge plus the length of the train. As shown in the figure:

Answer: As shown in the figure (similar schematic diagram can be drawn here), S train =L bridge +L train, then L train =S train -L bridge ①.

And because V train =54km/s=54÷3.6m/s= 15m/s, t= 1min20s=80s.

Then s train =V train × t =15m/s× 80s =1200m.

According to ①, then L train =S train -L bridge =1200m-1100m =100m.

Therefore, the length of the train is 100m.