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:

a)continue to move at 30 mph

b)eventually come to a stop

c)change its inertia

d)accelerate

If there is no net force acting on an object moving at a constant speed of 30 mph, then the object will continue to move at 30 mph.

Option A

Explanation:

As per Newton’s first laws of motion, an object will continue to stay in its state of motion or rest until an external unbalanced forces act on the object. So, it states that a moving objects will keep on moving unless and until a resisting forces act on it. Thus the required resisting force to stop object moving is termed as frictional force.

Similarly, if an object is at rest then it will stay at rest unless an external unbalanced forces are applied on the object and that force should be greater than the inertial force of the object. Thus, in the present case, an object moving with constant velocity at 30 mph will continue to move at 30 mph in the absence of net unbalanced force acting on the object.

it is the second option.