Question:
A block of mass $1 \mathrm{~kg}$ is placed at the point $A$ of a rough track shown in figure (8-E6). If slightly pushed towards right, it stops at the point B of the track. Calculate the work done by the frictional force on the block during its transit from $A$ to $B$.
Solution:
Work done = change in P.E.
$\mathrm{W}=\mathrm{mgh}-\mathrm{mgH}$
$W=1 \times 10 \times(0.8-1)$
$W=-2 \mathrm{~J}$