The following problems are based on the topic Work Energy Theorem.
Example WET.1: An Object of mass m is tied to a string of length l and a variable force F is applied on it which brings the string gradually at angle θwith the vertical. Find the work done by the force F.
Solution WET.1: STEP 1: Draw a rough sketch if possible STEP 2: Solution In this case three forces are acting on the object:
- Tension (T)
- weight (mg) and
- applied force (F)
Using Work Energy Theorem,
Further, , as tension is always perpendicular to displacement. or
NOTE: the applied force F is variable. So, if we do not apply Work energy theorem here we will have to use method of integration.