let us say that there is a coil of copper hanging from the ceiling so that its radius is parallel to the ceiling and its height perpendicular. let's also say that there is a current going through the coil such that the magnetic force inside the coil points upward. now let's say that an iron bar with the same height of the coil is suspended inside, held up by the magnetic force. there are m tethers attaching the coil to the iron bar radially, evenly spaced throughout the height of the coil. what is the force on tether k < m and the force on the first k tethers?