A block of mass 'm', kept on a horizontal surface, is moved through a distance 's' by applying a horizontal…
A block of mass 'm', kept on a horizontal surface, is moved through a distance 's'
by applying a horizontal force (F) to it. What is the work done by the normal
reaction?
$\frac{\mathrm{F}}{\mathrm{s}}$
$\mathrm{Fs}$
zero
$\frac{\mathrm{S}}{\mathrm{F}}$
Solution
In the first case, the centre of gravity is at a height $=\frac{b}{2}$ $\therefore$ Work done $=\mathrm{mgh}=\mathrm{mg}\left(\frac{b}{2}\right)$
In the second case, the height of the centre of gravity $=\frac{L}{2}$
$\therefore$ Work done $=m g \frac{L}{2} \therefore L>b$
$\therefore$ Extra work done $\quad=m g\left(\frac{L-b}{2}\right)$