Question

Astronaut Flo wishes to travel to a star 20 light years away and return. Her husband Malcolm, who was the same age as Flo when she departs, stays home (baking cookies). If Flo travels at a constand speed of 80% of the speed of light (except for a short time to turn around), how much younger than Malcolm will Flo be when she returns?

Hint--How long does Malcolm sit around baking cookies? How far is the distance to Flo?

Answer 1

distance = 20 year * c

same distance flo has to travel with speed 0.8c

0.8c = 20 year * speed of light / time

time = 20 / 0.8

time = 25 years

time took to return = 25 years

total time taken = 50 years

by time dialation formula

t' = t / sqrt(1 - (v/c)^2)

t' = 50 / sqrt(1 - 0.8^2)

t' = 83.33 years

flo will be 83.33 - 50 years younger

flo will be 33.33 years younger