Thanks all for your help. I came up with a solution,
Just to clarify the question. The part am analysing does not come into contact with the floor. It's a sheet metal part mounted inside a rugged plastic case (Pelicase). The sheet metal deflects when the plastic case hits the floor.
My solution was to guess the deflection and use it to calculate the impact force. I then compared the deflection from Creo simulate to my guessed deflection. From this I made a better guess of the deflection and run the analysis again. I did this till I got the accurate deflection.