Why Is Energy Conservation Not Valid in Moving Frames?

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SUMMARY

The discussion centers on the application of energy conservation principles in non-inertial frames, specifically in the context of a collision involving blocks A and B. When analyzed from the moving frame of block B, the initial mechanical energy calculated is 12J, which leads to confusion regarding energy conservation. The key conclusion is that energy conservation does not hold in non-inertial frames due to the differing kinetic energy perceptions, as demonstrated by the movement of block C. This discrepancy arises because kinetic energy is frame-dependent, particularly in non-inertial frames where additional forces may come into play.

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Jahnavi
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Homework Statement


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Homework Equations

The Attempt at a Solution



If I work in the lab frame I get the correct answer 4J .

But I do not understand why I do not get the correct answer if I work in the moving frame of block B .

After collision with block A , block B starts moving with 2m/s towards right .

Now in the frame of B , initial velocity of C is 2m/s towards left . Total initial mechanical energy = (1/2)(6)(22) = 12J .

In this frame spring will have maximum compression when C is at rest .That means maximum potential energy should be 12 J .

What is the mistake ?

The same problem arises if I work in the frame of block C .

So why is it that energy conservation is not holding true in the moving frames ?
 

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Jahnavi said:
the moving frame of block B .
That will not be an inertial frame. KE appears different in different frames, even inertial ones, so in a non-inertial frame it will not be conserved.
 
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