Describe how a multistage fitness test works and what it is intended to do

Using the work energy theorem. what is the velocity of a 850kg car after starting at rest when 13,000j of work is done to it.

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,?

Where do magnetic lines of force enter earth?