Physics - W.E.P. Question with Solution | TestHub

Key Idea The energy lost due to air friction is equal to difference of initial kinetic energy and final potential energy. Initially body posses only kinetic energy and after attaining a height the kinetic energy is zero. Therefore, loss of energy $=\mathrm{KE}-\mathrm{PE}$ $$\begin{array}{rl}& =\frac{1}{2}{\mathrm{mv}}^2-\mathrm{mgh}\\ & =\frac{1}{2}\times 1\times 400-1\times 18\times 10\\ & =200-180=20\mathrm{J}\end{array}$$