Exam-style question
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A spaceship has a contracted length of 80 m as measured by an observer on Earth. If the spaceship is moving at 0.6c relative to Earth, what is its proper length?.
- A.80 m
- B.100 m
- C.80/0.6
- D.80*0.6
Model answer
What a good answer should say
- 100 m
Explanation
Why this works
Formula: L = L0 √(1 - v²/c²). Substitution: L = 80 m, v = 0.6c.
Working: L0 = L / √(1 - v²/c²) = 80 m / √(1 - 0.36) = 80 m / √0.64 = 80 m / 0.8 = 100 m. Units: m.
Conclusion: The proper length is 100 m.
Common mistake
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