Work Energy Theorem: Practice Problem & Solution

Solution Explained:

To solve this problem, we apply the core principles of Work Energy Theorem. Understanding the underlying formula is key to arriving at the correct answer below:

By work-energy theorem, the work done by air resistance plus gravity equals change in kinetic energy. Since it returns to the same level, net work by gravity is zero. Thus, work done by air resistance is $W = \Delta K = \frac{1}{2}m(v^2 - u^2) = 3750\text{ J}$.