Arolling ball has an initial velocity of 5 meters per second. 30 seconds later, its velocity is 2 meters per second. what is the acceleration of the ball?

Acceleration is defined as the velocity of an object over a period of time.
Mathematically, 
Acceleration, A = Velocity [V] /Time [T]
From the question given above, we are told that 
T = 30 seconds
Initial velocity, V1 = 5
Final velocity, V2 = 2
Change in velocity, V = V1 - V2 = 5 - 2 =3 
A = V / T = 3 / 30 = 0.1
Therefore A = 0.1 m/s^2.