The law of conservation of energy states that energy may neither be produced nor destroyed. Therefore the amount of all the energies in the system is a constant.
Energy Conservation, At Point A

A stone of mass 10 gram is placed at the top of a tower 50 m high and it is allowed to fall freely. Find out the energy conservation at points A, B and C?
Mass of stone = 10g = 10/1000 kg = 0.001 kg. Acceleration due to gravity,g = 9.8 m/s^{2} Height = 50 m
Energy Conservation At Point A,B,C
Substitute the given values in the formula,
Energy Conservation At Point 'A'P.E at A  = mgh 
= 0.01 x 9.8 x 50  
= 0.01 x 98 x 5  
= 4.9 J 
K.E at A  = 1/2 mv^{2} 
=1/2 m * 0 (stone is at rest)  
= 0 
Total energy at A = P.E + K.E= 4.9 + 0 = 4.9 J
Energy Conservation At Point 'B'Height from the ground = 40 m
P.E at B  = mgh 
= 0.01 x 9.8 x 40  
= 0.01 x 98 x 4  
= 3.92 J 
K.E at B = 1/2 mv^{2} To calculate v we make use of 3^{rd} equation of motion
,v^{2}=u^{2}+2gSu=0 (u is the initial velocity of a moving stone) v^{2}=0+2*9.8*10 v^{2}=196
Therefore, K.E at B  = 1/2 * 0.01 * 196 
= 0.98 
Total energy at B = P.E + K.E= 3.92 + 0.98 = 4.9 J
Energy Conservation At Point 'C'Height from the ground = 0 m
P.E at C  = mgh 
= 0.01 x 9.8 x 0  
=0 J 
K.E at B = 1/2 mv^{2} To calculate v we make use of 3^{rd} equation of motion,
v^{2}=u^{2}+2gSu=0 (u is the initial velocity of a moving stone) v^{2}=0+2*9.8*50 v^{2}=980
Therefore, K.E at C  = 1/2 * 0.01 * 980 
= 4.9 
Total energy at C = P.E + K.E= 0 + 4.9 = 4.9 J The total energy at A, B and C is 4.9 J. This means the law of conservation of energy holds good in the case of an object falling freely under gravity.