In a velocity-time graph, if the velocity is constant, are the forces acting on the object balanced or unbalanced?

In a velocity-time graph, if the velocity is constant, are the forces acting on the object balanced or unbalanced?

• A. Unbalanced
• B. Balanced
• C. Cannot be determined
• D. Zero velocity

Answer: (B)

Constant velocity means there is no change in speed or direction, so acceleration is zero. According to Newton’s second law, the net force equals mass times acceleration, and with zero acceleration the net force must be zero. That’s what it means for forces to be balanced: all forces present cancel each other out so their total is zero, even though individual forces might still act. On a velocity-time graph, a horizontal line indicates velocity is not changing, which is exactly zero acceleration. So the forces must sum to zero. Why the other ideas don’t fit: if the forces were unbalanced, there would be a nonzero acceleration and the graph would show a sloped line. The question provides constant velocity, so you can determine the net force is zero; “cannot be determined” isn’t right because the graph gives you the needed information. And zero velocity is only one possible special case of constant velocity; a constant, nonzero velocity is still consistent with balanced forces.

Constant velocity means there is no change in speed or direction, so acceleration is zero. According to Newton’s second law, the net force equals mass times acceleration, and with zero acceleration the net force must be zero. That’s what it means for forces to be balanced: all forces present cancel each other out so their total is zero, even though individual forces might still act.

On a velocity-time graph, a horizontal line indicates velocity is not changing, which is exactly zero acceleration. So the forces must sum to zero.

Why the other ideas don’t fit: if the forces were unbalanced, there would be a nonzero acceleration and the graph would show a sloped line. The question provides constant velocity, so you can determine the net force is zero; “cannot be determined” isn’t right because the graph gives you the needed information. And zero velocity is only one possible special case of constant velocity; a constant, nonzero velocity is still consistent with balanced forces.