If the velocity of the object changes from

If the velocity of the object changes from 5 cm / sec to 15 cm / sec in 5 seconds, then at what average rate is the velocity changing?

It requires 3.1 seconds, starting from rest, for a ball to roll the 68 centimeter length of a uniform 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 ball?

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

At what average rate does the velocity of an airplane change, if it accelerates uniformly down a runway, starting from rest, requiring 12 seconds to cover a distance of 200 meters.