The second statement is the correct choice. Don't make me type it out.
F = ma
a = f/m
if f doubled , acc. will be doubled
KE= 1/2 mv^2
Kinetic Energy is equal to 1/2 x mass x velocity squared
The mass of the larger ball has TWICE
the kinetic energy. KE is directly proportional to the mass.
Density applies to many if not all aspects of life. With density you can explain why ice floats. You can explain why oxygen is on the earth, and not floating around in space( or being replaced by another gas). You can also explain why heat rises while cold air sinks.