## 87. Math Puzzle $8 / 72$

A screw comes loose from a wheel with a diameter of $20 \mathrm{~cm}$, which makes 600 revolutions per minute, and flies straight up.

How high does it fly?
The screw wound around the circumference of the wheel has a speed

$$
v=\frac{\text { circumference }}{\text { time for one revolution }}=\frac{20 \pi}{0.1}=6.28 \frac{\mathrm{m}}{\mathrm{s}}
$$

According to the law of conservation of energy $\frac{m}{2} v^{2}=m g h$, the screw will then fly $h=\frac{v^{2}}{2 g} \approx 2 \mathrm{~m}$ high.