According to newton�s first law of motion, if there is no net force (unbalanced forces) acting on an object that is moving at a constant 30 mph, the object will:

continue to move at 30 mph

eventually come to a stop

change its inertia

accelerate

Explanation:

Newton's first law of motion :

"Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces exerted on it."

From the question we know that the net forces on the object were zero or that the there were no unbalanced forces on it.

Therefore we can assume that the object is moving along a straight line.

And the object was moving at a constant speed of 30 mph.

So it is clear from the Newton's first law that the object will remain in the state of motion as it was earlier.

That is the object will remain in motion at constant speed of 30 mph.