A student builds the apparatus shown above. A light string is attached to an object of unknown mass and passed through a tube such that the other end of the string is attached to a second object of mass M M . By holding on to the tube, the student swings the object of unknown mass in a horizontal circle of radius r r while the object of mass M M hanging from the string remains at a constant height. In each trial, the radius r r of the circular path is changed and the tangential speed ν ν of the object of unknown mass is calculated. How can the student determine the value of the unknown mass by using the radius of its circular path and its speed?