Pakistan study notes for Matric, Intermediate, B.A, B.COM BSC, M.A, BCS. Free Pakistani Urdu educational school, colleges and University notes.



According to the law of conservation of energy,

“Energy can neither be created nor it is destroyed, however energy can be converted from one form energy to any other form of energy”.


Prove the law of conservation of energy


Let us consider an example of a body of mass “m” lying at height above the ground At point A body is at rest so its initial velocity is zero.

Suppose the body is released from height “h” and after covering distance of Mx” it velocity become “V” at Point B Now we check the total energy at point a and b


Energy Conservation At Point ‘A’

At point A the velocity of body is zero so its Kinetic energy is zero but it has some Potential energy


Total energy = Kinetic Energy + Potential Energy

T.E = K.E + P.E

T.E = 0 + mgh

T.E = mgh ——– 1

Energy Conservation at Point ‘B’

At point B the velocity is “V” so its Kinetic Energy is ½ mv2 but now first we calculate V

We have

Vi = 0

S = x

a = g

V = ?


According to 3rd equation of motion

2aS     = Vf2 – Vi2

2gx      = v2 – 02

2gx      = v2      ————- 2


K.E      = is ½ mv2

K.E      = ½ m 2 gx

K.E      = mgx ————– 3



Total energy = Kinetic Energy + Potential Energy

T.E = K.E + P.E

T.E = mgx + mg(h – x)

T.E = mgx + mgh – mgx

T.E = mgh      4


Equation 1 and 4 show that the total energy at Point A and B are same so the law of conservation of energy is proved

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