Physics
posted by Morgan .
Okay, I saw this one previously posted, but the answer it kept leading me to was wrong.
A sports car of mass 1400kg (including the driver) crosses the rounded top of a hill (radius 88m) at 23 m/s. Find the normal force exerted by road on the car.
I thought that the normal force was mass times acceleration, just what the road is doing to the car. So I multiplied 9.8 times 1400, but that was wrong. What am i doing wrong? The same applies to a driver (weighing 75kg in the car)

normal force= apparent weight
= mgmv^2/r 
So, basically, the way I can look at problems like these is to subtract the two accelerations (normal's gravity and centripetal) then multiply them by the mass (F=ma)?

yes.

Why is the centripetal force subtracted from the force of gravity? Aren't both going in the same direction (since centripetal force is always in the direction of the center of the circle)