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Q: The work done by the force of friction is..........
  • A. always positive
  • B. positive only for small frictional forces
  • C. always negative
  • D. positive only for large frictional forces
Correct Answer: Option C - Frictional force is always opposite to the relative motion of the body. When a body is dragged along the rough surface, the frictional force will be acting in the direction opposite to the displacement. The angle between the friction force and the displacement of the body will 180⁰. Thus, the work done by the frictional force will be negative.
C. Frictional force is always opposite to the relative motion of the body. When a body is dragged along the rough surface, the frictional force will be acting in the direction opposite to the displacement. The angle between the friction force and the displacement of the body will 180⁰. Thus, the work done by the frictional force will be negative.

Explanations:

Frictional force is always opposite to the relative motion of the body. When a body is dragged along the rough surface, the frictional force will be acting in the direction opposite to the displacement. The angle between the friction force and the displacement of the body will 180⁰. Thus, the work done by the frictional force will be negative.