Q 13

The closest known star to our solar system is Alpha Centauri,which is approximately 4.30 light years away. A spaceship with a constant speed of 0.800c relative to the earth travels from Earth to this star.
(a)How much time would elapse during the trip on a clock on board the spaceship?
(b)How much time would elapse during the trip on a clock on Earth?

Q 14

A spaceship approaches the earth with a speed 0.50c.A passenger in the spaceship measures his heartbeat as 70 beats per minute.What is his heartbeat rate according to an observer that is at rest relative to the earth?
A) 69 beats per minute
B) 73 beats per minute
C) 65 beats per minute
D) 61 beats per minute
E) 80 beats per minute

Q 15

A set of twins,Andrea and Courtney,are initially 10 years old. While Courtney remains on Earth,Andrea rides on a spaceship which travels away from Earth at a speed of 0.60c for five years (as measured by Courtney),then immediately turns around and comes back at 0.60c. When Andrea returns,Courtney is 20 years old. How old is Andrea upon her return?
A) 10 y
B) 12 y
C) 15 y
D) 18 y
E) 20 y