Exam-style question
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If an experimenter on Earth measures a light beam traveling at 3.0×10^8 m/s, what can a second experimenter moving at 0.1c relative to Earth conclude about the speed of that same beam?.
- A.It is 2.7×10^8 m/s.
- B.It is 3.0×10^8 m/s.
- C.It is 3.3×10^8 m/s.
- D.It depends on the direction.
Model answer
What a good answer should say
- It is 3.0×10^8 m/s.
Explanation
Why this works
Formula/Rule: Constancy of the speed of light – all inertial observers measure the same speed c. Substitution: moving observer at 0.1c.
Working: The moving observer’s measurement is unaffected by their motion; they still record 3.0×10^8 m/s. Answer: It is 3.0×10^8 m/s.
Units/Conclusion: m s⁻¹.
Common mistake
No common mistake is linked to this question yet.