If the velocity of the object changes from

If the velocity of the object changes from 3 cm / sec to 11 cm / sec in 9 seconds, then at what average rate is the velocity changing?

A ball rolling from rest down a constant incline requires 8.6 seconds to roll the 68 centimeter 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 ball?

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

An automobile accelerates uniformly down a constant incline, starting from rest. It requires 15 seconds to cover a distance of 172 meters. At what average rate is the velocity of the automobile therefore changing?