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Need some expertice on rotational motion

Q) a 250kg roller coaster travels on along track as shown*** at point A and B the coaster is traveling along circular paths. the speed at point A is 20m/s what is the max speed the coaster can have at B and still remain on the track.
*** ill do my best to describe this track....basically looks like one half circle the bottom half, meaning concave up, with point A at the bottom, Radius = 10m....then that half circle is attached to another. bigger half circle but this time the upper half, meaning concave down, with point B on top. Radius equals 15m....imagine drawing an S on a paper then turning it 90 degrees to the left, thats what it looks like... ok so i had to find the force of n at point A,,, i got that part, but now, it wants to know max speed at point B, so i thinks to myself this...
(m)(Ac)= normal force + mg at point B

so 250 * ((V)^2)/15 = normal force + 250(9.8)

how do i calculate n??? i did try working backwards...using the velocity at point A and trying to find speed where the 2 half circles meet, then trying to find velocity at point B....not sure if thats how to do this problem, but if it is, then i also need help finding the velocity for point B... any help is greatly appriciated
FALSE ALARM..... i just busted the MEi +Wnc= MEf equation on this mofo and got my velocity at point B, man this was a tricky problem.....sorry to spam the boards...........................IM THE SMARTEST MAN ALIVE

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