If body M, with a positive charge, is used to charge body N by induction, what will be the nature of the charge left on the latter?

a. must be equal in magnitude to that on M
b. must be negative
c. must be positived. must be greater in magnitude than that on M

what's the answer and why ??

During the experiment if you could triple the breakaway magnetic force with all other quantities left unchanged, what is the new value for the critical velocity if it was v0 (initial velocity), initially? (b) now if you halved the radius with all other quantities left unchanged, what is the new critical velocity if it was v0 (initial velocity), initially? (c) if during the experiment, critical velocity quadrupled with all other quantities left unchanged, what is the new breakaway force if its magnitude was initially f0,?