If the velocity of the object changes from

If the velocity of the object changes from 4 cm / sec to 16 cm / sec in 12 seconds, then at what average rate is the velocity changing?

A cart rolling from rest down a constant incline of length 52 cm requires 3.2 seconds to travel length of the incline.

What is its average velocity?

An object which accelerates uniformly from rest will attain a final velocity which is double its average velocity.

What therefore is the final velocity of this cart?

What average rate is the velocity of the cart therefore changing?

At what average rate does the velocity of an automobile change, if it accelerates uniformly down a track, starting from rest, and if it requires 13 seconds to cover a distance of 128 meters.