To determine what will happen to the nail based on the action-reaction pair, consider the scenario involving the nail. If only one force is acting on the nail, you should assess whether this force is balanced by other forces or not.
- If there is an unbalanced force acting on the nail (for example, if the nail is being hammered downward but there are no equal and opposite forces acting upwards to counteract this force), the nail will accelerate downward.
- If all the forces acting on the nail are balanced (the force down is equal to the force up), then the nail will remain at rest.
Given your options:
- If there are unbalanced forces acting on the nail => b. accelerate downward because there are unbalanced forces.
- If all forces acting on the nail are balanced => a. remain at rest because the forces are balanced.
Without more context, if the nail is just being described with regard to a force acting upon it without mention of balancing forces, option b would most likely be accurate assuming an external force like a hammer is being applied to it.
So, the correct choice based on common scenarios would be:
b. accelerate downward because there are unbalanced forces.