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"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.

Please help


This must be a coaching material or the book of some indian author who by default mean that "pulling slowly" implies that we don't change the velocity. I also experienced the same difficulty. If preparing for Jee just accept this as a fact as it would be never specified


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