Work done by the force of friction is____________________?
Correct answer: B. always negative
- A. always positive
- B. always negative
- C. positive only for small frictional force
- D. positive only for large frictional force
Explanation
For ordinary friction opposing the motion, the angle between friction and displacement is 180°, so W = Fs cos 180° = -Fs, making the work negative. The likely wrong choice is c because the sign of frictional work does not depend on whether the frictional force is small or large.
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About Work
Work is done when a force produces displacement, with its value determined by the component of force along the displacement. The topic covers positive, negative and zero work, work by variable forces from force-displacement graphs, and the connection between net work and change in kinetic energy.
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Work is a: