An unstable particle is created in the upper atmosphere from a cosmic ray and travels straight down toward the surface of the earth with a speed of 0.99542 c relative to the earth. a scientist at rest on the earth's surface measures that the particle is created at an altitude of 47.0 km .
part a as measured by the scientist, how much time does it take the particle to travel the 47.0 km to the surface of the earth?