To analyze this problem, let’s calculate the car's speed for each time segment and its average speed over the entire journey.

1. First Segment: The car travels 15 km every 10 minutes for the first hour.

   • Total time: 1 hour (60 minutes).
   • Distance covered: Since it travels 15 km every 10 minutes, in 60 minutes it travels: $\frac{60}{10} \times 15 = 6 \times 15 = 90 \text{ km}$

2. Second Segment: The car travels 45 km in the next 30 minutes (or 0.5 hours).

   • Distance covered: 45 km
   • Time taken: 0.5 hours (30 minutes)

3. Total Distance and Total Time:

   • Total distance covered = 90 km + 45 km = 135 km
   • Total time taken = 1 hour + 0.5 hour = 1.5 hours

4. Average Speed Calculation: $\text{Average speed} = \frac{\text{Total distance}}{\text{Total time}} = \frac{135 \text{ km}}{1.5 \text{ hours}} = 90 \text{ km/h}$

Summary

The car's average speed over the entire journey is 90 km/h.

Would you like a breakdown of the steps, or have any specific questions?

Here are five related questions that explore this topic further:

1. What would the average speed be if the car took an extra 15 minutes in the second segment?
2. How would the distance change if the car traveled at 20 km every 10 minutes in the first hour?
3. How does the car’s speed compare if it maintained a constant speed throughout the trip?
4. If the journey was split into three equal parts with varied speeds, what would the average speed be?
5. What would be the car’s average speed if the second segment covered 60 km instead?

Tip: Average speed is always calculated by dividing total distance by total time, not by averaging the speeds of different segments.