A. attract each other.
The Law of Universal Gravitation discusses the phenomenon of gravity. Remember that gravity is the force that keeps us on Earth; the Earth pulls us down, and our bodies pull back. Gravity is the force of attraction, so the correct answer is a).
The acceleration of the object is 
Explanation:
We can solve the problem by using Newton's second law, which states that the net force exerted on an object is equal to the product between the mass of the object and its acceleration:

where
F is the net force
m is the mass of the object
a is its acceleration
For the object in this problem,
F = 500 N is the applied force
m = 75 kg is the force
Solving the equation for a, we find the acceleration:

Learn more about Newton's second law:
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A. Made of the marble.
the mass remains constant when you drop the marble but the rest of the variables change as the marble is dropped, therefore, the only constant variable is its mass.