A circular curve of a highway is designed for traffic moving at $72 \mathrm{km} {\mathrm{h}}^{-1}$. If the radius of the curved path is $100 \mathrm{m}$, the correct angle of banking of the road should be given by

A car travels with a constant speed on a circular road on level ground. In the figure shown, $F_{\mathrm{air}}$ is the force of air resistance on the car. Which of the other forces best represents the horizontal force of the road on the car's tyres?

A $2 \mathrm{kg}$ block is gently pushed from rest at $\mathrm{A}$ and it slides down along the fixed smooth circular surface. If the attached spring has a force constant $\mathrm{k}=20 \mathrm{N} {\mathrm{m}}^{-1}$, then what is the unstretched length of the spring so that it does not allow the block to leave the surface until the angle with the vertical is $\mathrm{\theta }={60}^{°}$?