Hello:)!
I don’t really understand the uniform deceleration too :/

Deceleration is the opposite of acceleration.

The mathematical formula for deceleration is:

Uniform deceleration of an object can be defined as  decreasing the velocity of an object in equal amount in an equal interval of time.

The graph attached below shows a constant decrease in the velocity with a uniform time interval.

force required to detach it is given by

charges are taken to be fundamental charge

now we have

so above is the minimum distance at which it will detach