Problem: You are riding in an elevator on the way to the eighteenth floor of your dormitory. Near the end of your upward trip, while the elevator is going up and slowing down, the magnitude of the elevator's acceleration is a = 1.87m/s^2. Beside you is the box containing your new computer; box and contents have a total mass of 28.0kg. While the elevator has the described acceleration, you push horizontally on the box to slide it at constant speed toward the elevator door.

Part A: If the coefficient of kinetic friction between the box and elevator floor is µk = 0.32, what magnitude of force must you apply?

I need help to determine what magnitude of force you apply.