A school bus travels 120 km in the first 2 hours of a trip and 80 km in the next 2 hours. (a) Is the motion uniform or non-uniform? (b) What is the average speed for the whole trip? Step 1: Check equal intervals. In the first 2-hour interval the bus covers 120 km; in the second equal 2-hour interval it covers only 80 km. The distances in equal time intervals are unequal. Step 2: Conclusion for (a): the motion is non-uniform, because equal distances are not covered in equal intervals. Step 3: For (b), average speed = total distance / total time = (120 + 80) km / (2 + 2) h = 200 / 4 = 50 km/h. Answer: (a) Non-uniform motion. (b) Average speed = 50 km/h. Notice the average speed (50 km/h) hides the fact that the bus was faster in the first half and slower in the second — that is why we also study instantaneous speed.