5.2. A boy presses a vertical rod against a rough horizontal surface with his thumb. Then he gradually tilts the rod, keeping the component of the force directed along the rod applied to its end unchanged. At an angle of inclination of the rod to the horizontal $\alpha=70^{\circ}$, the rod starts to slide along the surface. Determine the coefficient of friction between the surface and the rod, if in the vertical position the normal reaction force of the plane was 21 times the weight of the rod. Round your answer to the hundredths.
5.2. A boy presses a vertical rod against a rough horizontal surface with his thumb. Then he gradually tilts the rod, keeping the component of the force directed along the rod applied to its end unchanged. At an angle of inclination of the rod to the horizontal $\alpha=70^{\circ}$, the rod starts to slide along the surface. Determine the coefficient of friction between the surface and the rod, if in the vertical position the normal reaction force of the plane was 21 times the weight of the rod. Round your answer to the hundredths.

Answer. $\{0,35\}$