Kinetic energy of N solid bodies

AI Thread Summary
The discussion centers on the kinetic energy equation for N solid bodies, specifically questioning the absence of the (1/2) factor in the kinetic energy formula presented in a book. The equation given is the sum of the differences in kinetic energy before and after a shock, but it lacks the standard (1/2) coefficient. Participants suggest that this omission could be a typo or an oversight by the author, although it does not affect the calculations since it is consistently absent from both sides of the equation. The consensus is that while the calculations remain valid, the author should have clarified this omission. Overall, the missing factor raises concerns about accuracy in the presentation of the physics concepts.
Oddbio
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This is a fairly simple question so I wasn't sure if it belongs here, but it is not a homework question. Just a question on something I'm reading.

The book says there are N solid bodies with initial speed vi (i=1, 2, 3, ..., N)
and final speed vi' after some shock to the system.

The book then says that the difference in kinetic energy is:
\sum_{i=1}^{N}m_{i}(v_{i}'^{2}-v_{i}^{2})

But my question is, where did the (1/2) factor go from the kinetic energy?

I was even wondering if this has something to do with combining the sum for initial and final kinetic energies into a single script, but if I write the sum out using "j" for initial and "i" for final in the sums it comes out to be what they have but with a (1/2)... like I think it should.
Am I supposed to assume that this is just a typo? Even though several calculations are performed from that equation following its appearance.
I can't see any reason why it would be missing.
 
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Hi Oddbio! :smile:
Oddbio said:
But my question is, where did the (1/2) factor go from the kinetic energy?

Am I supposed to assume that this is just a typo? Even though several calculations are performed from that equation following its appearance.
I can't see any reason why it would be missing.

Typo (or laziness of the author)! :rolleyes:

I assume that it makes no difference to the calculations because it's missing from both sides of every equation.

But the author still shouldn't leave it out without warning. :frown:
 
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