Question 11:
moderateA bullet of mass $10\text{ g}$ leaves a rifle at an initial velocity of $100\text{ m/s}$ and strikes the earth at the same level with a velocity of $500\text{ m/s}$. The work done in joule overcoming the resistance of air will be:
(1989)
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 $W = \Delta K = \frac{1}{2}m(v^2 - u^2) = 3750\text{ J}$.