Which situation is contrary to Newton’s first law of motion? An object at rest begins to move when an external force is applied.
A moving object has a constant velocity under the influence of balanced forces.
An object at rest stays at rest as long as unbalanced forces act on it.
A moving object slows down when an external force is applied.

An object at rest stays at rest as long as unbalanced forces act on it.

Explanation:

Inertia can be defined as the tendency of an object or a body to continue in its state of motion or remain at rest unless acted upon by an external force.

In physics, Sir Isaac Newton's First Law of Motion is known as Law of Inertia and it states that, an object or a physical body in motion will continue in its state of motion at continuous velocity (the same speed and direction) or, if at rest, will remain at rest unless acted upon by an external force.

The inertia of a physical object such as a truck is greatly dependent or influenced by its mass; the higher the quantity of matter in a truck, the greater will be its tendency to continuously remain at rest.

Hence, the situation which is contrary to Newton’s first law of motion is that, an object at rest stays at rest as long as unbalanced forces act on it.

According to Newton’s first law of motion, an object at rest stays at rest as long as unbalanced forces do not act on it.

moving ball hits still ball. mover stops, hit ball moves. momentum transfer.