Gravity

Q. A chain of length L is released from rest, from a frictionless surface with half length hanging as shown in figure. Work done by gravity when the chain is just completely off the surface.
(m=10 kg, g=10 $m/s^2$ and L=10 $m$)

1. 475 J
2. 375 J
3. 250 J
4. 75 J