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SAI INTERNATIONAL SCHOOL
PHYSICS
CLASS IX
Chapter:WORK, ENERGY AND POWER
LESSON NOTES
Law of Conservation of Energy
It states that energy can neither be created nor destroyed, but it can be transformed
from one form to another.
The total energy before and after the transformation remains the same.
The total mechanical energy of an object remains constant during free fall.
Proof of Law of Conservation of Energy
Let a body of mass m falls from a point A, which is at a height h from the ground as
shown in the following figure:
At point A,
Kinetic energy Ek = 0
Potential energy Ep = mgh
Total energy, EA = Ep + Ek
⟹ EA = mgh + 0
⟹ EA = mgh
During the fall, after moving a distance x from A, the body has reached at B.
At point B,
Let the velocity at this point be v.
