Normal force on a banked road & why it's larger than the gravitational force here

Question

Please read this: http://www.askiitians.com/iit-jee-physics/mechanics/banking-of-roads.aspx

From my understanding of normal forces, they are a reaction to gravitational or other forces. When a force vertically applies to a surface, a normal force comes along and balances it.

The way I imagine it should be, is gravitational force Mg has its perpendicular component cancelled by N, while its parallel-to-surface component provides the centripetal force, but that gives my questions wrong answers. It would be nice if someone could tell me why.

Also, going by what my books are telling me, everything makes sense--a larger N could balance Mg and also provide centripetal accelleration, but the questions is why. Why is N larger. What causes this 'reaction' force to be larger than the applied force Mg?

A lot of people say that the centripetal force has to apply, and only two forces are at play--N or Mg, so (1) Why not get the centripetal force from Mg like I wrote above? (2) The curved block doesn't know that centripetal force must be applied. Why is it exerting N larger than Mg in the first place?

Answer 1

When the car takes the curve, think at the circle it goes on as a polygon with an infinite number of sides. Instead of continuing to go straight, the ground acts on the object with a force that increases the normal force and creates the centripetal force needed for the object to go circularly.