The correct answer is:

B. Equal to the product $ma$

Explanation:

According to Newton's Second Law of Motion, the sum of all forces acting on an object, often referred to as the "net force," must be equal to the mass of the object ($m$) multiplied by its acceleration ($a$). This can be represented by the formula:

$F_{\text{net}} = ma$

If an object is in motion, it does not necessarily mean that the net force is zero. The net force is zero only if the object is moving at a constant velocity, meaning no acceleration (in which case $a = 0$). If the object is accelerating, there must be a net force acting on it, which will be equal to $ma$.

Other Options:

• Option A: The net force being equal to the object's weight would only apply if the object were in free fall with no other forces acting on it.
• Option C: The net force is zero only if the object is at rest or moving at constant velocity (no acceleration).
• Option D: We can indeed determine the sum of the forces based on Newton’s laws, so this option is incorrect.

Would you like further details or have questions?

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Here are 5 related questions for further exploration:

1. What happens to an object if the net force acting on it is zero?
2. How does Newton's First Law relate to the concept of net force?
3. What factors influence the acceleration of an object given a constant net force?
4. Can an object be in motion if the net force is zero? Explain.
5. How do balanced and unbalanced forces affect the motion of an object?

Tip: Always remember that the presence of a net force causes acceleration, not necessarily movement itself!