Question:
An unruly demonstrator lifts a stone of mass $200 \mathrm{~g}$ from the ground and throws it at his opponent. At the time of projection, the stone is $150 \mathrm{~cm}$ above the ground and has a speed of $3.00 \mathrm{~m} / \mathrm{s}$. Calculate the work done by the demonstrator during the process. If it takes one second for the demonstrator to lift the stone and throw, what horsepower does he use?
Solution:
Work done $\mathrm{W}=\mathrm{mgh}+^{\frac{1}{2}} \mathrm{mv}^{2}$
$W=0.2 \times 9.8 \times 1.5+\left({ }^{\frac{1}{2}} \times 0.2 \times 3^{2}\right)$
$W=3.84 \mathrm{~J}$
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