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**1. The problem statement, all variables and given/known data**

The diagram below shows a roller coaster ride which contains a circular loop of radius r. A car of mass m begins at rest from point A and moves down the frictionless track from A to B where it then enters the vertical loop (also frictionless), travelling once around the circle from B to C to D to E and back to B, after which it travels along the flat portion of the track from B to F (which is not frictionless).

1. Find the centripetal acceleration of the car at points B and C.

2. Find the normal force at point B.

**2. Relevant equations**

Fnet = mv^2/r

ac = v^2/r

**3. The attempt at a solution**

1. I got Ac = Fn/m - g for point B. For point C i got Ac = -Fn/m + g

2. I got Fn = mv^2/r + g

I got -2 marks off for this problem.. where did I go wrong?

By the way, the loop goes counter clockwise (B, C, D, E)