A ladder rests against a smooth wall. The wall exerts a force on the ladder that is
- A. along the ladder
- B. vertically upwards
- C. perpendicular to the wall
- D. parallel to the wall
Explanation
A smooth surface can exert no friction, so the only force it can apply is the normal reaction, which by definition acts at right angles to the surface. That makes the reaction from a vertical wall horizontal. The ground, being rough, supplies both a normal force and the friction that stops the ladder sliding out.
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