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I'm staring down a concept homework assignment that is giving me fits. We are just moving into relativity.

6) The quantity γmc^2 represents...

a) the rest mass energy.

b) relativistic kinetic energy.

c) total relativistic energy.

d) relativistic momentum.

e) None of the above.

I can't find this in my textbook, but mc^2 is the rest energy. So I thought that must be a. But γ is the symbol for a photon, and a couple of other things. I might be second guessing myself with e.

11) Which of the following (if any) is/are is NOT relativistically invariant?

a) Mass.

b) Speed of light.

c) Momentum.

d) Space-time interval.

e) All of the above are relativistic invariants.

f) None of the above are relativistic invariants.

Relativistic variants are the stuff that changes at relativistic speeds. So relativistic invariants are the stuff that DOESN'T change at relativistic speeds. The stuff that is NOT relativistic invariants are relativistic variants. So I am looking for stuff that changes at relativistic speeds. The speed of light can't ever change so it can't be B, which also eliminates E. Mass doesn't change, but there is a relativistic mass...I'm not sure if that means mass changes or perhaps just the effect of mass changes. Whatever happens to mass, so happens momentum. Space-time travel definitely changes at relativistic speeds (time dilation and length contraction).

So, relativistic variants (A, C, D) and relativistic invariants (B). I thought the answer would be A C and D but that isn't an option. So I think I've either misunderstood my relativity chapter or I'm argued myself into a loop somewhere along the way.

12) Which of the following do NOT use general relativity in calculations?

a) Describing black holes.

b) Global positioning.

c) Gravitational lensing.

d) Describing neutron stars.

e) All of the above employ general relativity calcultions.

The chapter discusses that GPS is an application of the special theory of relativity. But I thought that the special theory was more specific than general. But none of the others are in my text, but I know that general relativity talks about gravity and stuff which is relative (get it...relative...HAH!) to A C and D. So I really think that it's E and that general relativity actually does describe GPS.

Help? I've been working on this for far too long and my brain is just fried! Thanks!

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# General Relativity Concepts

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