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# An object of mass m is lied to a string of length l and a variable horizontal force is applied on it which is initially zero and gradually increases until the string makes an angle $\theta$ with the vertical. Work done by the force F is

$(a)\;mg(1-\sin \theta) l \quad (b)\;mgl \quad (c)\; mgl(1+\cos \theta) \quad (d)\;mgl (1-\cos \theta)$

Work done by force =Less in potential energy
$W_F=+mgh$
$\qquad= +mgl(1-\cos \theta)$
Hence d is the correct answer

edited Feb 17, 2014 by meena.p

+1 vote