a turn of a the wheel is simply the length or perimeter of the wheel, namely the circumference of the circular wheel.
[tex]\bf \textit{circumference of a circle}\\\\ C=2d~~ \begin{cases} d=diameter\\[-0.5em] \hrulefill\\ d=25 \end{cases}\implies C=2(25)\implies C=50\implies \stackrel{\textit{two turns}}{C = 100}~in[/tex]
