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Does the work energy theorem always and absolutely deals with change in kinetic energy or in some cases with change in mechanical energy? There is a sum of gravitation A person brings a mass of 1 kg from infinity to a point A. Initially it was at rest but as it reaches A velocity becomes 2m/s . The work done by the peron on the mass is -3J the potential at A is a) -3 b) -5 Ans is b) What I have done is loss in P.E + Gain in K.E = work done I.e -GMm/R + 1/2mv^2 = -3 -GMm/R+ 2 = -3 So p.e is -5 It will be extremely helpful if you say if my concept is clear or somewhere faulty. Will look forward eagerly for an explicit explanation.

Does the work energy theorem always and absolutely deals with change in kinetic energy or in some cases with change in mechanical energy? 
There is a sum of gravitation 
A person brings a mass of 1 kg from infinity  to a point A. Initially it was at rest but as it reaches A velocity becomes 2m/s . The work done by the peron on the mass is -3J the potential at A is
a) -3
b) -5
Ans is b) 
What I have done is loss in P.E + Gain in K.E = work done
I.e 
-GMm/R + 1/2mv^2 = -3
-GMm/R+ 2 = -3
So p.e is -5
It will be extremely helpful if you say if my concept is clear or somewhere faulty. Will look forward eagerly for an explicit explanation.
 

Grade:12

2 Answers

Parth Kohli
24 Points
9 years ago
Yes, your logic works well! Work done on an object will contribute to its energy, which here is sum of the potential and kinetic energy. As we reach point A, its kinetic energy is 2 J, implying that the potential energy is -5 J, because you want the total energy to be -3 J. 
Chandra Chatterjee
22 Points
9 years ago
Thank you so much for the clarification

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