An object of mass $m$ is tied to a string of length $L$ and a variable horizontal force is applied on it which starts at zero and gradually increases until the string makes an angel $ heta$ with the vertical. Work done by the force $F$ is [image:6_image11.emf]

Question

An object of mass $m$ is tied to a string of length $L$ and a variable horizontal force is applied on it which starts at zero and gradually increases until the string makes an angel $	heta$ with the vertical. Work done by the force $F$ is [image:6_image11.emf]

Dr. Abubacker · Accepted Answer

(c) $W = \mathrm{\Delta}K$ or $W_{T} + W_{g} + W_{F} = 0$
(Since, change in kinetic energy is zero)
[image:6_image70.emf]
Here, $W_{T} =$ work done by tension = 0
$W_{g} =$ work done by fore of gravity
$= - mgh$
$= - mgL(1 - \cos	heta)$
$	herefore\ \ W_{F} = - W_{g} = mgL(1 - \cos	heta)$

Q. An object of mass $m$ is tied to a string of length $L$ and a variable horizontal force is applied on it which starts at zero and gradually increases until the string makes an angel $\theta$ with the vertical. Work done by the force $F$ is

Explanation

Reviewed by Dr. Abubacker

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