ANSWER:
F = m x a
STEP-BY-STEP EXPLANATION:
In the 3 exposed systems, we have in common that Newton's 2nd law applies, which establishes that if a net force is applied to an object, the speed of the object will change given that its direction or speed will change (acceleration), that the force varies according to the acceleration exerted on an object with stated mass.
Therefore, the common equation is:
[tex]F=m\cdot a[/tex]
