A toy is shown on the left. When the wheels of this toy rotate, the fan is also required to spin. If one pair of gears is to be used exclusively, which option will make this possible?
Show Hint
For gear-mechanism problems:
\begin{itemize}
\item Check the relative orientation of shafts,
\item Bevel gears are used for perpendicular axes,
\item Spur gears work only with parallel shafts.
\end{itemize}
Step 1: The wheels rotate about a \emph{horizontal axis}, while the fan rotates about a \emph{vertical axis}. Therefore, the gear pair must transmit motion between perpendicular shafts.
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Step 2: Such transmission requires gears whose teeth are designed to mesh at right angles, ensuring smooth rotation transfer without slipping.
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Step 3: Examine the options:
\begin{itemize}
\item A: Gears are not compatible for continuous perpendicular power transmission — invalid.
\item B: Uses bevel gears, which are specifically designed to transmit motion between perpendicular axes — valid.
\item C: Spur gears require parallel shafts — invalid.
\item Option D: Gear shapes do not allow proper meshing at right angles — invalid.
\end{itemize}
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Final Answer:
\[
\boxed{B}
\]
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