Ok,

A car of mass 1.5 tonnes pass over a bridge formed the arc of a circle of radius 20m.

a) Find the force exerted by the car on the road at the top of the bridge if the car is travelling at 10m/s.

b) What speed would cause the car to be on the point of lifting up off the bridge at its highest point

What I've done:

F = mv^2 / r

F = 1500 * 10^2 / 20

F = 7500 N

---- Don't know if this is anything (the answer in the book is 7200N)

tan(t) = v^2/rg

tan(t) = 10^2/20*9.8

tan(t) = 0.510

(t) = tan^-1(0.510)

(t) = 27.02 deg

Force of car on road = mg sin (t)

= 1500*9.8sin (27.02)

= 6678.23 N

However as I said previously the answer is 7200 N.

b) No idea really... not sure of the formula to use

The answer for b) is 14m/s.