As the velocity is constant, the result of the forces in the sled is zero. If [tex]T_x[/tex] is the horizontal component of the traction and [tex]F_{at}[/tex] is the frictional force:
[tex]F_R=0\iff T_x=F_{at}\iff T\cos30^o=\mu N\iff \\\\ T\cos30^o=\mu P\iff 200\cdot\dfrac{\sqrt3}{2}=\mu (500\cdot10)\iff 100\sqrt3=5000\mu\\\\\mu=\dfrac{100\sqrt3}{5000}\iff \mu=\dfrac{\sqrt3}{50}\Longrightarrow\boxed{\mu\approx0,035}[/tex]
