So the base in your question or problem it ask to find the minimum speed that the roller coaster must have to let the passenger don not fall out when travelling upside down and the circle has a radius of 7.6 m. So based on the diagram, the total force must equal the mass of the roller coaster times the quotient of Velocity and the square of the radius of the circle and with that itself, the minimum speed of the coaster must greater than zero
