1. The problem statement, all variables and given/known data Ringworld is an artificial world constructed in the shape of a giant ring that rotates around a star similar to our sun. The radius of the ring is 1.53x10^11m (from the sun to the ring). The mass of ringworld is 2.1x10^27kg and its simulated gravitational acceleration is 9.73m/s^2. Determine how fast the inner surface of the ringworld is moving to experience a "gravitational" (no idea why this is put in quotations in the question) acceleration of 9.73 m/s^2. Gravitational constant=6.67x10^-11 2. Relevant equations Vcentripetal=2πr/T Acentripetal=v^2/r or =4π^2(r)/T^2 F=Gm1m2/r^2 g=Gm/r^2 T1^2/R1^3=T2^2/R2^3 Any combination of the above also work. 3. The attempt at a solution How do you find the mass of the central body and the orbital period? It seems impossible to do anything without knowing one or the another. I don't know where to start. Any help is appreciated. Thanks.