please solve question 4.7........ .... ......... ..... ....... .....

use time period= 2pi*sqrt(I/MB) where I is moment of inertia and M is magnetic moment.magnetic moment= pole strength*length of magnet. and B is magnetic field in which they oscillate and is same throught out the experiment. so as M and are same for both only there moment of inertia difers and as masses are also same momnet of inertia is directly proportional to length of magnet. so answer is 1:2