# Change in kinetic energy of pendulum [closed]

"An object of mass m is tied to a string of length L and a variable horizontal force is applied on it which starts from rest and pulled slowly until the string makes an angle $$\theta$$ with the vertical. Find the work done by force F."

All the solutions that I have seen in such type of questions is by using work-energy theorem. $$\Delta U+ \Delta K= W$$

Here they take $$\Delta K$$ to be zero and calculate the change in potential energy and give the answer which turns out to be correct.

But I can't understand how $$\Delta K$$ is zero. Initially the body is at rest and some force is applied due to which it starts moving. Thus it gains some velocity.So there should be some change in Kinetic energy.