What is the force of the track on the car?

[ScullyX51]

Homework Statement

A roller-coaster has a mass of 500 kg when fully loaded with passengers. The car passes over a hill of radius 15 m. When at the top of the hill, the car has a speed of 8.0 m/s. WHat is the force of the track on the car at the top of the hill?

Homework Equations

F=ma

The Attempt at a Solution

I drew an FBD: wtih mg pointing down, N pointing up and static friction pointing to the left. ( I think this may be wrong, but I figured it may need static friction to stay on the track).
Then when broken into i and j components I got:
i= -M_sN=-MV²/r ...(because the acceleration is centripical)
then for j:
I have N-mg=0
N=mg
and since it was asking for the force of the track on the car, I thought this was the normal force, so I just plugged in the values for m ang, and got 4.9 kN up. This is wrong, it is saying the correct answer is 2.8 kN up. Any suggestions on where I went wrong?

 

[PhanthomJay]

The car is at the top of the hill; you seem to have your i and j mixed up. The centripetal accelertion is vertically down. Ignore friction.