How Does the Work-Kinetic Energy Theorem Apply When Raising a Ball Vertically?

[Spock007]

Assume a situation that there is a ball on the ground. A vertical force is applied to raise the ball to h at a constant speed. According to work-kinetic energy theorem, no net work is done on the ball owing to the constant speed. However, the potential energy increases as the ball gains elevation. The total energy does not seem conservative in this case. Why?

 

[Simon Bridge]

Welcome to PF;
The work-KE theorem you have been taught is wrong in general and can only be used in specific circumstances.
More completely, the work done on an object is equal to the change in it's mechanical energy. In this case: $W=\Delta K + \Delta U$