Question

which situation is contrary to newtons 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.

Explanation:

Newton's first law (law of inertia) states that an object at rest stays at rest, and an object in motion stays in motion with constant velocity, unless acted upon by a net (unbalanced) external force. Let's analyze each option:

• Option 1: An object at rest beginning to move when an external force is applied is consistent with Newton's first law (external force causes a change in state of rest).
• Option 2: A moving object having constant velocity under balanced forces is consistent (balanced forces mean no net force, so velocity remains constant).
• Option 3: An object at rest staying at rest with unbalanced forces acting on it is contrary. Unbalanced forces mean a net force, so the object should accelerate (change state from rest), but this option says it stays at rest.
• Option 4: A moving object slowing down when an external force is applied – if the external force is unbalanced (e.g., friction), it causes deceleration, but wait, no – wait, Newton's first law: a net external force causes a change in motion. But "slowing down when an external force is applied" – if the force is unbalanced, it's a change (deceleration), but the key is option 3: unbalanced forces on a resting object should make it move, but option 3 says it stays at rest, which is contrary. Wait, re - evaluating:

Wait, Newton's first law: if net force (unbalanced forces) acts, the object's motion changes (acceleration). So for an object at rest, unbalanced forces should make it move. Option 3 says "An object at rest stays at rest as long as unbalanced forces act on it" – this is contrary to Newton's first law. Wait, but let's check the options again. Wait, the question is which is contrary. Let's re - express Newton's first law:

• If net force = 0 (balanced forces): object at rest stays at rest; object in motion stays in motion with constant velocity.
• If net force ≠ 0 (unbalanced forces): object accelerates (changes velocity: speed up, slow down, change direction).

Now let's analyze each option:

• Option 1: Object at rest, external force (so net force ≠ 0) applied – object begins to move. This is consistent (net force causes acceleration from rest).
• Option 2: Moving object, balanced forces (net force = 0) – constant velocity. Consistent.
• Option 3: Object at rest, unbalanced forces (net force ≠ 0) act – object stays at rest. Contrary (net force should cause acceleration, so object should move, not stay at rest).
• Option 4: Moving object, external force (net force ≠ 0) applied – slows down. This is consistent (net force causes deceleration, a change in motion).

So the situation contrary to Newton's first law is option 3: "An object at rest stays at rest as long as unbalanced forces act on it."

Answer:

C. An object at rest stays at rest as long as unbalanced forces act on it (assuming the options are labeled as follows: A. An object at rest begins to move when an external force is applied. B. A moving object has a constant velocity under the influence of balanced forces. C. An object at rest stays at rest as long as unbalanced forces act on it. D. A moving object slows down when an external force is applied.)