How Can Kinetic Energy Change with Zero Net Work?

[madah12]

Homework Statement

There is something I don't understand in work energy theorem
If we push on a box on a horizontal surface with force F to cause it to move with displacement x with constant velocity that means the force by friction is equal to F right? so the total work is the net force times the displacement which is zero
but the box was initially at rest then it is moving with constant velocity so there is change in kinetic energy
so how can there be change in kinetic energy with zero work?

Homework Equations

The Attempt at a Solution

 

[The legend]

when the body is moving with constant velocity, there is no change in constant velocity.

Also, for the body to start from rest, it needs a little more force (if you notice that coefficient of static friction is more than kinetic)...

 

[madah12]

Then in the time interval from just before you applied the force till it moved with constant velocity we can't actually say the total work is 0 right?

 

[The legend]

exactly.