The work performed by a frictional force is always____________________?
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Answer: B. always negative
Explanation
Frictional force always acts in the direction opposing object movement. Displacement and opposing friction vectors form a one hundred eighty degree angle. The cosine of one hundred eighty degrees is negative one, making work negative. Friction is a non conservative force that dissipates mechanical energy into heat. Negative work indicates that energy is being removed from the moving object. Work equation W equals F d cos theta yields negative values for opposing forces.
Braking systems in automobiles use friction to remove kinetic energy and stop safely. Mechanical machinery loses efficiency over time due to persistent sliding friction forces. Walking forward relies on static friction performing zero work while feet rest. Always positive work contradicts the opposing direction of frictional forces. Positive only for small friction ignores the directional angle entirely in math. Positive only for large friction is physically impossible for opposing resistance forces.
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