Question

question 9 (1 point)
a large rock is motionless on a flat sidewalk. which statement best explains why the rock remains motionless?
○ a the forces acting on the rock are all balanced.
○ b the only force acting on the rock is directed toward the sidewalk.
○ c there are no forces acting on the rock.
○ d the sidewalk exerts an unbalanced force on the rock.

Explanation:

According to Newton's first law of motion, an object at rest will remain at rest if the net force acting on it is zero. When forces are balanced, the net force is zero.

• Option a: If the forces acting on the rock are balanced, the net force is zero. So, the rock will remain motionless. This is in line with Newton's first law.
• Option b: There are at least two forces acting on the rock - gravitational force (acting downward) and normal force (exerted by the sidewalk, acting upward). So, it is incorrect to say the only force is directed toward the sidewalk.
• Option c: There are forces acting on the rock (gravitational force and normal force). So, this option is wrong.
• Option d: If the sidewalk exerted an unbalanced force, there would be a net force, and the rock would accelerate (not remain motionless). So, this option is incorrect.

Answer:

A. The forces acting on the rock are all balanced.