Answer:
Stars are at large distances that even light takes thousands of years to reach us from there.
for example, alpha centauri is 4300 light years away from earth and it is considered the nearest star to us, this means that light from there takes 4300 years to reach us and with a spaceships that can move with the speed of light is would take us 4300 years to get there which is imposible to live for that long.
hence, it is difficult to move between the stars.
Mechanical energy
I think
Crystalline solids must have a specific, orderly arrangement of atoms to be considered so.
2,450 Joules, kinetic energy is 1/2 mass x velocity squared.
Most likely climbing up the mountain
