Question

A law enforcement officer in an intergalactic "police car" turns on a red flashing light and sees it generate a flash every 1.5 s. A person on earth measures that the time between flashes is 2.9 s. How fast is the "police car" moving relative to the earth?

Answer 1

Solve this equation for v:

2.9 = 1.5 / sqrt [1 - (v/c)]^2

c is the speed of light.

This is one of Einstein's relativity equations

Answer 2

0.8c