[填空题]
A bicyclist traveling with speed v=4.2m/s on a flat road is makij(mp yq ef01fxesu0q ,jl:+ )ong a turn with ay: l)0(f,f1omj+jusqqp 0e xe alg2(ik-6hk3 hiw-o; pvpoi/ radius The forces acting on the cyclist and cycle are the normal for vak og2io /hh3kp;w6(-ii-plce $\left(\mathbf{\vec{F}}_{\mathrm{N}}\right)$ and friction force $\left(\mathbf{\vec{F}}_{\mathbf{fr}}\right)$ exerted by the road on the tires, and $m\vec{\mathbf{g}}$ the total weight of the cyclist and cycle (see Fig. 8–56). (a) Explain carefully why the angle $\theta$ the bicycle makes with the vertical (Fig. 8–56) must be given by tan $\tan\theta=F_{\mathrm{fr}}/F_{\mathrm{N}}$ if the cyclist is to maintain balance.(round to the nearest integer) (b) Calculate $\theta$ for the values given. $^{\circ} $ (c) If the coefficient of static friction between tires and road is $\mu_s=0.70$ what is the minimum turning radius? m