Newton’s first law states that if an objects velocity is changing a must be acting on it.
a) force
b) mass
c) acceleration
d) inertia

(a)

Explanation Newtons First Law can be written as the formula

since acceleration is the changing of velocity as its formula is

Thus, a force must be acting on an accelerating/decelerating object

It is not mass as the mass does not act on the object but rather the mass is acting on the surface of the ground.Changing velocity is already acceleration inertia is the term used to describe Newtons first law

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