Answer:
-1500 m/s2
Explanation:
So the ball velocity changes from 10m/s into the wall to -8m/s in a totally opposite direction within a time span of 0.012s. Then we can calculate the average acceleration of the ball as the change in velocity over a unit of time.

- Speed is the rate of change of distance with time while velocity is the rate of change of displacement with time.
- Speed is a scalar quantity while velocity is a vector quantity.
- Speed cannot be negative but velocity can be negative.
Hope you could get an idea from here.
Doubt clarification - use comment section.
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