A spaceman, who weighs 75 kg on the Earth, is in a room of a spaceship that is rotating around the axis through the centre of the spaceship with angular speed $\displaystyle \omega = 0,5 rad/s$. The spaceman is on a weight scale and he sees that he weighs 70 kg. At what distance he is from the axe of rotation?

How can I deal with this problem? I don't know what formula use!