The end of a chain of length (L) and mass (ho) per unit length which is piled

Question:

The end of a chain of length $L$ and mass $ho$ per unit length which is piled on a platform is lifted vertically with a constant velocity $v$ by a variable force $P$. Find $P$ as a function of the height $x$ of the end above the platform. Also find the energy lost during the lifting of the chain.

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