Well first of all, a planet doesn't have a semimajor axis, although it's orbit does.
In an orbit with a smaller semimajor axis, the planet moves faster, and its orbital period is shorter.
That's why the International Space Station circles the Earth in less time than the Moon does.
Answer:
I think it is difficult to determine what has caused climate change in the distant past because it must have been a long time ago so geologists can't carry out different experiments and figure out what gases the planet had conjured, so geologists can only make predictions based off the evidence they currently have from what the planet looked like before. The planet must have changed over the years, therefore the climate has also changed in the future, so they cannot work with how the planet looked in the past.
Answer:
-611.32 N/C
0.43723 m
Explanation:
k = Coulomb constant = 
q = Charge = -4.25 nC
r = Distance from particle = 0.25 m
Electric field is given by

The magnitude is 611.32 N/C
The electric field will point straight down as the sign is negative towards the particle.

The distance from the electric field is 1.71436 m
Whan object is at equilibrium, then the forces are balanced. Balanced is the key word that is used to describe equilibrium situations.