Galaxies are sprawling systems of dust, gas, dark matter, and anywhere from a million to a trillion stars that are held together by gravity. Nearly all large galaxies are thought to also contain supermassive black holes at their centers.
Answer:
Conservation of momentum.
Momentum is zero after collision, no direction or speed.
Explanation:

So the dimensions of acceleration is

Any answer that comes under that definition is correct.
Complete Question:
A coin is dropped off of a building landing on its side. It hits with a pressure of 400 N/m². It hits with a force of 0.1N. Calculate the area of the coin?
Answer:
Area = 0.00025 m²
Explanation:
Given the following data;
Pressure = 400N/m²
Force = 0.1N
To find the area of the coin;
Pressure = Force/area
Area = Force/pressure
Substituting into the equation, we have;
Area = 0.1/400
Area = 0.00025 m²