6.2 A wheel with a diameter of 80 mm rotates at \( 1260 \mathrm{r} / \mathrm{min} \). Calculate: 6.2.1 The rotational frequency in \( \mathrm{r} / \mathrm{s} \).

To convert the rotational speed from revolutions per minute (r/min) to revolutions per second (r/s), you divide by 60 (since there are 60 seconds in a minute). So, for a wheel rotating at 1260 r/min, the calculation is: \[ \text{Rotational frequency} = \frac{1260 \, \mathrm{r/min}}{60} = 21 \, \mathrm{r/s} \] Therefore, the rotational frequency of the wheel is \( 21 \, \mathrm{r/s} \).