Time Speed Distance

Relative speed is the speed of one object as observed from another moving object. If two objects move in the same direction, the relative speed is the difference between their speeds. If they move towards each other (opposite directions), the relative speed is the sum of their speeds. For example, if a thief runs at 10 km/h and a policeman chases at 12 km/h, the policeman closes the gap at a relative speed of 2 km/h.

Average speed is NOT the simple average of speeds. It is the total distance traveled divided by the total time taken. This is a common trap in exams. For instance, if you go from A to B at 40 km/h and return at 60 km/h, your average speed is not 50 km/h. You must use the total distance and total time calculation, or the special formula for equal distances.

These problems involve finding the distance when a person reaches a destination at two different times based on two different speeds. The key is to find the difference in time. If a person is 5 minutes late at speed S1 and 5 minutes early at speed S2, the total time difference is 10 minutes. This difference is then equated to the difference in time formulas (D/S1 - D/S2).