When nina jumps into the air, the earth pulls her back down through the force of

1) WRONG. Since gravitational force is an attractive force.
2) WRONG. The Earth does accelerate but the acceleration is so small that it's negligible. However it DOES ACCELERATE.
3) CORRECT.
4) WRONG. Mass means gravitational field, so Nina might be small compared to the Earth but it still creates a gravitational field around her. This answer is also wrong because it's breaking Newton's third law of action-reaction. If Earth pulls Nina, then Nina pulls the Earth back with the same force. Yes, with the SAME FORCE, however F=m*a, so the great difference in mass makes Nina's acceleration much bigger than the Earth's one.

Gpe = 30000J

Explanation:

Given the following data;

Weight = 100N

Height = 300m

To find the gravitational potential energy (gpe);

Gravitational potential energy can be defined as an energy possessed by an object or body due to its position above the earth surface.

Mathematically, potential energy is given by the formula;

Where,

G.P.E represents potential energy measured in Joules.

m represents the mass of an object.

g represents acceleration due to gravity measured in meters per seconds square.

h represents the height measured in meters.

Gpe = mgh

But weight = mg = 100N

Substituting into the equation, we have:

Gpe = 100*300

Gpe = 30000J