An unwary football player collides with a padded goalpost while running at a velocity of 8.50 m/s and comes to a full stop after compressing the padding and his body 0.210 m. (a)
What is his deceleration in m/s2? (Enter the magnitude.)
m/s2
(b)
How long in seconds does the collision last?

diagram is missing, but i will try to explain your doubt.

answer:

amplitude is the maximum displacement or distance moved on a point of a vibrating body or wave measured from its equilibrium position.it is equal to half the length of vibration path.

it is a negative acceleration

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