Question

A block of mass 1 kg is placed at point A of a rough track shown in figure (8-E6). If slightly pushed towards right, it stops at point B of the track. Calculate the work done by the frictional force on the block during its transit from A to B.
Figure

Answer 1

$$\begin{gathered} \mathrm{Given}, \\ \mathrm{Mass}\mathrm{of}\mathrm{the}\mathrm{block},m=1\mathrm{kg} \\ \mathrm{Height}\mathrm{of}\mathrm{point}\mathrm{A},H=1\mathrm{m} \\ \mathrm{Height}\mathrm{of}\mathrm{point}\mathrm{B},h=0.8\mathrm{m} \end{gathered}$$

Work done by friction = Change in potential energy of the body
$$\begin{gathered} \Rightarrow {\mathrm{W}}_1=mgh-mg\mathrm{H} \\ =1\times 10\left(0.8-1\right) \\ =-1\times 10\times \left(0.2\right)=-2\mathrm{J} \end{gathered}$$

The work done by the frictional force on the block during its transit from A to B is $-$2 joule.