Four identical pallets of bricks, each with a mass of 40 kg with a square cross-sectional area of 0.50 m2, are stacked on the floor. What is the change in height of the pallet at the bottom of the stack if the pallets are 5.0 m tall when not stacked

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,?