Answer the following questions about mass and weight in space travel:
a. (i) Define mass and weight.
b. (ii) Explain why astronauts orbiting Earth in a spacecraft feel almost weightless even though Earth’s gravitational pull acts on them.
c. (iii) An astronaut has a mass of 80 kg. Describe, without calculation, whether his mass and his weight change when he moves from Earth to the Moon. Give a reason for each case.