A block of mass M is hanging over a smooth and light pulley through a light string. The other end of the string is pulled by a constant force F. The kinetic energy of the block increases by 20J in 1s. Which of the following statements is correct?
Correct answer: B. The tension in the string is F.
- A. The tension in the string is Mg.
- B. The tension in the string is F.
- C. The work done by the tension on the block is 20J in 1s.
- D. The work done by the force of gravity is 20J in 1s
Explanation
Option B is correct as the tension in the string is F and not Mg. The work done by all the forces (in this case the tension and the force of gravity) is equal to the change in kinetic energy. Net work done on the body is equal to the gain in kinetic energy of the block. Thus increase in kinetic energy in 1s=Work done by tension on the block in 1s+Work done by gravity on the block in 1s.
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Work transfers energy when a force causes displacement, while kinetic energy, gravitational potential energy and power describe motion, position and the rate of energy transfer. The work-energy theorem links net work with change in kinetic energy, and efficiency accounts for energy losses rather than treating them as energy destruction.
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