A chain of mass M and length L is initially held in vertical position as shown in the figure. It is released from rest, then which of the following graph(s) is/are correct. Here N represents normal force by the ground on the chain and v represents velocity of free end

Consider an elemental part of length dx at height x from floor. Just before hiting the floor, its velocity is v=2gx  and  mass element is dm=MLdx. After hiting floor this element comes to rest.​∴Fimpulsive=dPdt=0−dm2gxdtAt this moment the length of heap of chain on floor is x.​∴Fheap=MLxg​Thus, N=Fheap+Fimpulsive=MgxL+2MgxL=3MgxL=2gxdmdt=2gxMLdxdt=2gxML2gx=2MgxLCase 1 : 0L​N=Mg​Whole chain is on the floor and N becomes constant.