List the forces acting on a block resting on a horizontal surface with no vertical acceleration.

List the forces acting on a block resting on a horizontal surface with no vertical acceleration.

• A. Gravity downward; Normal force upward; Friction along the surface if present
• B. Gravity upward; Normal force downward; no friction
• C. Normal force only; gravity is balanced in the horizontal direction
• D. There are no forces acting on a block at rest

Answer: (A)

When a block sits on a horizontal surface with no vertical acceleration, the forces in the vertical direction must balance: gravity pulls downward, and the surface pushes upward with a normal force. Along the surface, friction can act if there’s a tendency or force to slide, but if there’s no horizontal force, friction is zero. So the forces you’d expect are gravity downward, the normal force upward, and friction along the surface if there’s any chance of horizontal motion. This matches the described description: gravity downward; normal force upward; friction along the surface if present. The other options mix up directions or omit forces, which doesn’t fit the situation.

When a block sits on a horizontal surface with no vertical acceleration, the forces in the vertical direction must balance: gravity pulls downward, and the surface pushes upward with a normal force. Along the surface, friction can act if there’s a tendency or force to slide, but if there’s no horizontal force, friction is zero. So the forces you’d expect are gravity downward, the normal force upward, and friction along the surface if there’s any chance of horizontal motion. This matches the described description: gravity downward; normal force upward; friction along the surface if present. The other options mix up directions or omit forces, which doesn’t fit the situation.