Single correct option
A stone tied to a string is whirled in a horizontal circle with uniform speed. The work done by the tension in the string in one complete revolution is
- A. zero
- B. equal to the kinetic energy of the stone
- C. equal to tension multiplied by the circumference
- D. negative of the kinetic energy of the stone
Show answer and solution
Answer: (A) zero
Tension acts along the radius towards the centre while the displacement at every instant is along the tangent, so the angle between force and displacement is 90 degrees and W = F d cos 90° = 0. The kinetic energy is constant because speed is constant, so by the work-energy theorem the net work is zero. Multiplying force by circumference ignores the direction.
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