This seems to be a topic of kinematics in junior high school physics. . .

Let the acceleration be a and the movement time be t, from the meaning of the question, we can get: (the movement distance is s)

10=v=at

20 = s = 1/2 at 2 simultaneous equation: t = 4；; a=5/2

(1) scrolled for 4 seconds.

(2) The average reduction per second is 5/2 (m/s)

(3)S'= 1/2 at^2

15=0.5 * 2.5 * t^2