Which of the following speeds is the least?

The correct option is 50 meter / minute.

To determine which of the given speeds is the least, we need to compare them by converting all of them into a common unit. Let us convert each speed into meters per second (m/s).

1. First Option: 50 meter / second
This speed is already in meters per second:
Speed = 50 m/s

2. Second Option: 50 meter / minute
Since there are 60 seconds in 1 minute, we convert this speed as follows:
Speed = 50 meters 60 seconds ≈ 0.83 m/s

3. Third Option: 70 km / hour
To convert kilometers per hour to meters per second, we multiply by 1000 (to convert km to meters) and divide by 3600 (to convert hours to seconds):
Speed = 70 × 1000 meters 3600 seconds = 70 × 5 18 m/s ≈ 19.44 m/s

4. Fourth Option: 5 km / minute
To convert kilometers per minute to meters per second, we multiply by 1000 (to convert km to meters) and divide by 60 (to convert minutes to seconds):
Speed = 5 × 1000 meters 60 seconds = 5000 60 m/s ≈ 83.33 m/s

Comparing the values in the common unit (m/s):
- 50 m/s (First Option)
- 0.83 m/s (Second Option)
- 19.44 m/s (Third Option)
- 83.33 m/s (Fourth Option)

Clearly, 0.83 m/s is the smallest value among them. Therefore, 50 meter / minute is the least speed.