Step-by-step Solution:

Quick Solution

Part 1: Average Velocity

- Velocity is based on displacement, which is the straight-line distance from the start point to the end point.
- The body travels from A to B and then returns to A.
- Since the start and end points are the same, the total displacement for the journey is zero.
- Average Velocity = Total Displacement ÷ Total Time = 0 ÷ (10s + 5s) = 0 km/h.

Part 2: Average Speed

- Speed is based on the total distance traveled, regardless of direction.

1. Find the distance from A to B: - First, let's convert the speed to meters per second (m/s) by multiplying by 5/18.
- Speed (A to B) = 50 km/h × (5/18) = 125/9 m/s.
- Distance = Speed × Time = (125/9 m/s) × 10s = 1250/9 meters.

2. Calculate Total Distance and Total Time: - The body returns, so the total distance is twice the distance from A to B.
- Total Distance = 2 × (1250/9) = 2500/9 meters.
- Total Time = 10s + 5s = 15 seconds.

3. Calculate Average Speed: - Average Speed = Total Distance ÷ Total Time
- Average Speed = (2500/9) ÷ 15 = 2500 / (9 × 15) = 2500 / 135 ≈ 18.5 m/s.

Final Answer: The average speed is 18.5 m/s and the average velocity is 0 km/h.