Answer: When the Block's speed is at maximum
Step-by-step explanation:
From the formula of find acceleration
acceleration = speed/time
So we can tell that acceleration is directly proportional to speed
So when the speed reaches its maximum, acceleration is also maximum, when the speed starts reducing, acceleration also reduced,
Note: talking to account initial and final speed, if these are both the same, for a specific time, acceleration will become zero, because the change in velocity within that specific time is also zero