(A) Astronaut Sarah is traveling in a spaceship at a speed of 0.3c relative to a

Question

(A) Astronaut Sarah is traveling in a spaceship at a speed of 0.3c relative to an observer on Earth. She has a meter stick in the spaceship. What is the length of the meter stick as measured by Sarah?

A. 1.00 m

B. 0.96 m

C. 0.28 m

D. 1.28 m

(B) Sarah is changing the speed of her spaceship with respect to the Earth. Sandy, on the Earth, measures the length of the meter stick in Sarah's spaceship to be 0.6 m. What is Sarah's spaceship speed with respect to Earth?

A. 0.40c

B. 0.60c

C. 0.70c

D. 0.80c

E. 0.90c

A. 1.00 m

B. 0.96 m

C. 0.28 m

D. 1.28 m

Explanation / Answer

Part A)

Since Sarah is in motion with the meter stick, it does not change to her so it is 1 m long. That is choice A.

Part B)

Apply L = L'sqrt(1 - v^2/c^2)

.6 = 1sqrt (1 - v^2/3 X 10^8)^2

v = 2.4 X 10^8 m/s

Divide by 3 X 10^8 and get .8c

Choice D

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