Explain how a rapidly moving object have the same acceleration as a slowly moving one.

Yes they can have the same acceleration,

Explanation:

Think an object moving with velocity , and another object with velocity . After, the speed of first object is , and second object has speed .

And also acceleration is independent of speed, it is an increase in speed per second, so it can be same for rapidly moving as well as slowly moving.

We can think about gravitation acceleration it has same value for every object independent of speed, suppose two objects are at a height h, one of the object is dropped and another object is thrown downward with velocity v,so the gravitation acceleration will same for both independent of speed.

most voltage drop calculators want the distance between the source and destination. then internally, they double it so both the source and return wires are calculated. but you need to know which distance the calculator uses so you're not half of what you should be or double what you should be.

most circuit breakers will not take a #6 directly, so the electrician will have to splice on a smaller pigtail. you also have to upsize the grounding wire when you upsized the ungrounded (hot) wire (see note in 250.122). this will preclude using most cable assemblies, as a cable with #6 copper will most likely only have a #10 grounding conductor. you need a #6 grounding conductor if the circuit is 20a. a #8 cable is no better, as it will have a #10 grounding conductor too. but most 20a breakers will take a #8 directly.

in your related post, you didn't say what type of load this is. if it is a light or heater, voltage drop won't be a big issue. if this is a motor, the current needs are huge at startup and the voltage drop can pose a problem. if this is a motor, knowing if the motor is under much load during startup will answer the voltage drop effect (a saw is easier to start than a compressor).