A car is negotiating a curved road of mean radius R. The surface of the road is frictionless and it makes an angle θ with horizontal. Then the necessary centripetal force is supplied by the

Weight of the car is vertical and normal reaction N is normal to the road surface is shown in figure. So horizontal component of N is the horizontal radially inward force acting on the car and it supplies the necessary centripetal force.   Ncosθ=mg and Nsinθ=mv2r