Question

Explain the statement:
The work done by the tension in the string of a simple pendulum during one complete oscillation is equal to zero.

Answer 1

1. The term "Swing" simply means performing to and fro motion or oscillatory motion by the bob which is suspended by a string(mass less).​
2. Tension is a kind of pulling force that is transmitted throughout the entire length of the wire by each end of the wire.
3. Here the pulling force is developed due to weight(vertically downward)and force exerted by the point of suspension on the wire.
4. Now to calculate work done by tension force on the bob having mass m(say) we have to write $W=FScos\alpha$ where α is the angle between F(tension force on bob) and S(Displacement of bob). Here α is always 90° so, $cos\alpha =0$ hence $W=0$