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Question

A model aircraft internal-combustion engine produces 10 W of power. How much power is this in (a) lbf.ft/s and (b) hp?

Solution

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\begin{align*} {\color{#c34632}\text{(a)}}\;{\color{#4257b2}\text{Recall}:}\;&1\;\text{W}=\dfrac{1}{1055.056}\;\text{Btu/s}\\\\\ \therefore\;&10\;\text{W}=10\times \dfrac{1}{1055.056}\;\text{Btu/s}=\boxed{\dfrac{625}{65941}\;\text{Btu/s}}\\\\ {\color{#4257b2}\text{Recall}:}\;&1\;\text{Btu/s}=778.169\;\text{lb.ft/s}\;\\\\\ \therefore\;&10\;\text{W}=\dfrac{625}{65941}\times778.169\;\text{lb.ft/s}=7.376\;\text{lb.ft/s}\\\\ &\color{#19804f}\boxed{\color{#4257b2}10\;\text{W}=7.376\;\text{lb.ft/s}} \end{align*}

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