An object of mass m is tied to string of length L and a variable horizontal force is applied on it which starts at zero and gradually increases (it is pulled extremely slowly so that equilibrium exists at all times) until the string makes an angle θ with the vertical. Work done by the force F is :

Solution:
Be definition of Work, Work Done = F.S. cos θ
Taking S and cos θ together like
W= F. (S cos θ)= Force × Component of displacement along force
Here Force F is acting horizontally and displacement toward right is L sin θ, So
Work done = F.L. sin θ
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