Calculating Distance: Free Body Diagram for Box Sliding with Friction

[Shehryar]

Homework Statement

A 250 kg box slides down the ramp and then across a level floor. The coefficient of kinetic friction along the floor is 0.20. A person see the box moving at 1.0 m/s(left) and pushes on it with a horizontal force of 140 N (right). How far does the box travel before coming to rest?

I know that Fk = 0.20, m = 250g. Now I have to draw the free-body diagram.

2. The attempt at a solution
Initially, the diagram was like this:
<-------- v = -1.0m/sFa<------BOX----->Fa
----->Ft

Gravity and the normal force were also drawn, however, the diagram is wrong... For some reason, there is no Fa on the left side, but WHY? If the box was going off the ramp it has to have some force that is keeping it moving to the left? Can someone please explain how to draw the free body diagram, especially why there is no leftward force?

 

[haruspex]

If the box was going off the ramp it has to have some force that is keeping it moving to the left?

Not so. This is fundamental to kinetics. A body with no net force acting on it will keep moving with constant velocity.
Please clarify the meanings of your variables, Fk, Fa, Ft.