A star is 17.2 ly (light-years) from Earth. HINT (a) At what constant speed (in m/s) must a spacecraft travel on its journey to the star so that the Earth-star distance measured by an astronaut onboard the spacecraft is 4.06 ly? X m/s (b) What is the journey\'s travel time in years as measured by a person on Earth? yr (c) What is the journey\'s travel time in years as measured by the astronaut? yr Solution a)let Lo = 17.2 ly L = 4.6 ly let v is the speed of the spacecraft L = Lo*sqrt(1 - (v/c)^2) L/Lo = sqrt(1 - (v/c)^2 (L/Lo)^2 = 1 - (v/c)^2 (v/c)^2 = 1 - (L/Lo)^2 v = c*sqrt(1 - (L/Lo)^2) = 3*10^8*sqrt(1 - (4.05/17.2)^2) = 2.92*10^8 m/s b) T = Lo/v = 17.2*3*10^8/(2.92*10^8) = 17.67 years c) To = 4.06*3*10^8/(2.92*10^8) years = 4.17 years .