The speed at which the rider is spinning when the floor drops out beneath her is 5.42 m/s.
The acceleration of the rider when the normal force is half their weight is calculated as follows;
Fn = 0.5(W)
ma = 0.5 x mg
65 x a = 0.5 x 65 x 9.8
a = 0.5 x 9.8
a = 4.9 m/s²
a = v²/r
v² = ar
v = √ar
v = √(4.9 x 6)
v = 5.42 m/s
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