A teacher walks back and forth in front of the room during a lesson. He starts at one end of the desk and walk from the door to the window a distance of 4.0m in 5 s. Then he stops, turn around and walk 2.0 m back toward the door in 3 s. He stops here for 10 s and then walk 3 meters toward the door in 6 s. Deduce the average speed of the teacher over the entire 24 s interval?

0.375 m/s

Explanation:

The average speed of an object or a body is given by:

                      total distance traveled/total time taken

In the case of the teacher who walked back and fort:

Total distance traveled = 4.0 + 2.0 + 3 = 9 meters

Total time taken= 24 s

Hence,

Average speed of the teacher = 9/24

                             = 0.375 m/s

3. dark matter

empty space could also be a simple vacuum