Special relativity Flashcards

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1
Q
In a stationary reference frame on Earth, a 2 m rod is moving at half the speed of light.By how much does its length contract?
27 cm 
30 cm
25 cm
It does not contract
A

27 cm

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2
Q
You measure your car to be 5 m long.  How fast must you travel in your car for an outside observer to measure your car as being 4 m long?
A.  0.4 c
B.  0:6 c
C.  0:75 c
D.  0:8 c
A

0.6 c

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3
Q

You are on a platform at a train station, standing halfway between two clocks (A and B)that you observe to be synchronized. The clocks each emit a pulse of light when they strike 9:00am (in your reference frame). Since you are equidistant from the clocks, the pulses of light arrive at your location at the same time. At precisely 9:00am in your reference frame,a speeding train goes by at nearly the speed of light. The train travels in a direction parallel to the line joining the two clocks, and you observe that the train first passes in front of clock A, then in front of clock B (i.e. the train goes in the direction from A to B). Your physics professor, riding on the train, waves hello. What does your physics professor see?
Clock A emitted a pulse of light at the same time as clock B
Clock A emitted a pulse of light before clock B
Clock A emitted a pulse of light after clock B

A

Clock A emitted a pulse of light after clock B

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