A spaceship from another galaxy passes over the solar system directly above a radial line from the Sun to the Earth. (We measure that distance to be 1.5 × 1011 m.) On Earth, the spaceship is observed to be traveling at a speed of 0.80c, for which γ = 5/3. As measured on Earth it takes the spaceship 625 seconds to travel from the Sun to Earth. When a scientist in the spaceship measures the Earth-Sun distance and the time it takes her to travel that distance, she finds the results are, respectively
A)9.0 × 1010 m; 375 s.
B)9.0 × 1010 m; 625 s.
C)1.5 × 1011 m; 625 s.
D)2.5 × 1011 m; 625 s.
E)2.5 × 1011 m; 1042 s.

Question

Quizplus · Accepted Answer

The correct answer is A because the spaceship is traveling at a speed of 0.80c, for which γ = 5/3. As measured on Earth it takes the spaceship 625 seconds to travel from the Sun to Earth. So, the distance between the Earth and the Sun as measured by the spaceship is:d = v * t = (0.80c) * (625 s) = 9.0 × 1010 mThe time it takes the spaceship to travel from the Sun to Earth as measured by the spaceship is:t' = t / γ = 625 s / (5/3) = 375 s

A Spaceship from Another Galaxy Passes Over the Solar System