To prove that $\bar{v}_I = \bar{v}_{II} = \bar{v}_{III}$ under uniform traffic conditions, we need to establish that the average speed of traffic flow is the same for different segments of road or different groups of vehicles. Let's go through the proof step-by-step.

Definitions

1. Uniform Traffic Condition: This means that the spacing between vehicles is constant, and the speed of each vehicle is also constant, i.e., $v_i(x) = v_i(t) = v$.

2. Average Speeds:

   • $\bar{v}_I$: Average speed for the first segment or group.
   • $\bar{v}_{II}$: Average speed for the second segment or group.
   • $\bar{v}_{III}$: Average speed for the third segment or group.

Proof

1. Constant Speed Assumption: Under uniform traffic conditions, every vehicle $i$ travels at the same constant speed $v$. That is, for any vehicle $i$: $v_i(x) = v_i(t) = v$ This means that the speed of any vehicle does not vary with time or position.

2. Average Speed Calculation: The average speed $\bar{v}$ for any segment or group is given by the sum of the speeds of all vehicles in that segment or group divided by the number of vehicles in that segment or group.

   $\bar{v} = \frac{\sum_{i=1}^{N} v_i}{N}$ Since $v_i = v$ for all $i$, this simplifies to: $\bar{v} = \frac{N \cdot v}{N} = v$ This is true for any segment or group of vehicles.

3. Equality of Average Speeds: Since $\bar{v}_I$, $\bar{v}_{II}$, and $\bar{v}_{III}$ are calculated in the same way and all vehicles have the same speed $v$, we have: $\bar{v}_I = \bar{v}_{II} = \bar{v}_{III} = v$

Hence, under uniform traffic conditions with constant vehicle spacing and speed, the average speeds for different segments or groups are equal, i.e., $\bar{v}_I = \bar{v}_{II} = \bar{v}_{III}$.

Questions

1. What happens to the average speed if one vehicle in a segment has a slightly different speed?
2. How would this proof change if the spacing between vehicles is not constant?
3. Can we generalize this proof to non-uniform traffic conditions?
4. What role does the density of traffic play in determining the average speed?
5. How would introducing acceleration affect the average speed calculation?

Tip

When working with uniform motion scenarios, it's crucial to remember that constant speed implies no acceleration or deceleration, making all time and position variables interchangeable for speed calculations.