I think it's more complicated than that.
The platform pushes the player to the right, while the player is on the platform must receive an impulse, when the player leaves the platform the impulse must be gradually reduced.
The player controls must be affected by the impulse.
That is not achieved by altering the value of "deceleration".
This is what I got but here the controls are not affected by the momentum of the platform.
dropbox.com/s/dgpfi46avwg502j/test.capx