Then the speed change is 8-(- 10)= 18.
The average acceleration is a =18/0.1=180 (m/s 2).
Obviously, the direction A is positive and the initial velocity direction is negative, so the direction is different.
The reason is that in the process of collision, the force acting on the ball in the speed direction is only the reaction force given by the wall, which is opposite to the initial speed direction, so the acceleration direction is opposite to the initial speed direction.
2. First, when the initial velocity is 0, a = 0.2m/s 2 is calculated according to the displacement formula S = 1/2 at two places.
The speed of the first 10 second at = 2m/s.
According to the displacement formula s = vt+ 1/2at 2-(T is the speed from the end of 10 seconds to the end of 20 seconds, and v means the end of 10 seconds).
s = 2 * 10+ 1/2 * 0.2 * 10^2=20+0.5*0.2* 100=30m