Relativity II PREFLIGHT

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Relativity

1.

Since Einstein's special theory of relativity changes the way we think about speed, it changes any equation that has speed in it, such as momentum and kinetic energy. By using the theorems of the conservation of momentum and energy, and applying them in all reference frames, one can show that the momentum can be written:
p = mv
and the total energy (the one that is conserved)
E = mc2
From this form of the equation, we see that a stationary object has a relativistic correction of 1, retrieving Einstein's most famous equation. Some of the homework problems are related to the question of how much mass is converted to energy in an atom bomb. Let me ask a more philosophical question: How did this equation (and the terrors of nuclear war) arise from the extremely simple 2 postulates of relativity? How did rest mass and relativity get magically connected?




2.

What is the ratio of kinetic energy to total energy (K/E) of a 0.511 MeV electron compared to a 940MeV proton?

Electron ratio is greater than proton.

Equal.

Electron ratio is smaller than proton's.


3.

The police officer pulled over a speeding physics student and said he had run a red light. The student objected and said that the Doppler effect caused the light to appear green as he approached it. If the student was not speeding, then what was the speed of light in his universe?




honors extra

Estimate the mass of uranium that would be consumed every second if the U.S. power grid were completely run by nuclear power plants. I estimate the US power needs at 10 TW. How much uranium is used up in an entire year?





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