A body initially at rest and sliding along a frictionless track from a height h: NEET 2018 Physics

A body initially at rest and sliding along a frictionless track from a height h(as shown in the figure) just completes a vertical circle of diameter AB=D. The height h is equal to.
Solution:
Let total energy is conserved,
Total mechanical energy at start = Total mechanical energy at 'B'

For detailed explanation about:
The law of conservation of energy
Law of Conservation of Mechanical Energy
Significance of frictionless track(path)