M=mass of the plate
What is the block made of, does it have a spring behind it to cushion the shock?
How fast is the plate traveling?
I have not checked this site but I would immagine there are equations for determining the acceleration or in this case dceleration of the plate.
If the block is solid with no "give", then things get a litttle more complex as you need to calculate impulse or "shock" loading and the forces can get high fast.
Hope this points you in the right direction.