Question:
A block of mass $30.0 \mathrm{~kg}$ is being brought down by a chain. If the block acquires a speed of $40.0 \mathrm{~cm} / \mathrm{s}$ in dropping down $2.00 \mathrm{~m}$, find the work done by the chain during the process.
Solution:
$v^{2}-u^{2}=2 a s$
$a=\left(0.4^{2}-0\right) / 2 \times 2$
$a=0.04 \mathrm{~m} / \mathrm{s}^{2}$.
Force
$\mathrm{F}=\mathrm{ma}-\mathrm{mg}$
and
Work done
$W=F s \cos \theta=m(a-g) s \cos \theta$
$W=30(0.04-9.8) \times 2 \times 1$
$W=-585.5 \mathrm{~J} \approx-586 \mathrm{~J}$
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