GRE Subject Test: Physics : Four Vectors

Study concepts, example questions & explanations for GRE Subject Test: Physics

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Example Questions

Example Question #1 : Four Vectors

A reference frame S' is moving at 0.6c in the z direction with respect to a stationary frame S.  An event occurs in S' with the coordinates (x', y', z', ct')=(1, 0, 2, 3).  What are the coordinates (x, y, z, ct) of the event with respect to the stationary frame S?

Possible Answers:

(1, 0, 3.3, 2.64)

(1, 0, 4.75, 5.25)

(1, 0, 5.25, 4.75)

(1, 0, 2.64, 3.3)

(1, 0, 2, 3)

Correct answer:

(1, 0, 4.75, 5.25)

Explanation:

To apply a Lorentz transformation, we need gamma and beta:

Then, apply the Lorentz transformation:

 

Example Question #2 : Four Vectors

A container of water is carried on a space ship traveling at 60% the speed of light relative to the Earth. From the perspective of an observer on Earth, what is the speed of the light in the water?

Possible Answers:

Correct answer:

Explanation:

The speed of light through water in a stationary frame is found from the index of refraction of water, which is approximately 

To find the relative speed, use the following equation:

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