Law of conversation of energy (By pak physics notes)

Law of conversation of energy
This law state the
       '' Energy can neither be destroyed nor be created but can change from one form to anotheer''
Proof by simple pandulam

Energy at point ''A''


At point ‘A’ velocity of the bob of simple pendulum is zero. Therefore, K.E. at point ‘A’ = 0. Since the bob is at a height (h), Therefore, P.E. of the bob will be maximum. i.e.
P.E. = mgh.
Energy total = K.E. + P.E
Energy total = 0 + mgh
Energy total = mgh This shows that at point A total energy is potential energy.


Energy at point ''M''


If we release the bob of pendulum from point ‘A’, velocity of bob gradually increases, but the height of bob will decreases from point to the point. At point ‘M’ velocity will become maximum and the height will be nearly equal to zero.
Thus ,
K.E. = maximum = 1/2mV² but P.E. = 0.
Energy total = K.E. + P.E
Energy total = 1/2mV² + 0
Energy total = 1/2mV²
This shows that the P.E. at point is completely converted into K.E. at point ‘M’.


Energy at point ''B''


At point M the bob of Pendulum will not stop but due to inertia, the bob will moves toward the point ‘B’. As the bob moves from ‘M’ to ‘B’, its velocity gradually decreases but the height increases. At point ‘B’ velocity of the bob will become zero.
Thus K.E. at point ‘B’ = 0 but P.E. = max.
P.E. = mgh.
Energy total = K.E. + P.E. 
Energy total = 0 + mgh
Energy total = mgh
This shows that at point B total energy is again potential energy.


                                      
                                       (www.pak-physicsnotes.blogspot.com)

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