(Solved): See Figure below: A 68.8 kg roller coaster starts from rest at point A and slides down the frictio ...

See Figure below: A 68.8 kg roller coaster starts from rest at point A and slides down the frictionless loop-the-loop shown in the Figure. Height of point $B$ is $D=5.6$ meters. How hard does the track press against the car at point B (give answer in Newton and use the upward direction as positive)?