Hangzhou chunzhao

A, by F=BIL, I =BLv0 12R, the ampere force is fa = I=BLv0R, so a is correct;

B, because ampere force always does negative work to MN, it produces Joule heat. When the rod reaches the leftmost end for the first time, the average speed of the rod is the largest and the average ampere force is the largest. Joule heat generated by the whole circuit should be greater than 43Q, so B is correct;

C, when the rod returns to the initial position again, the speed is less than v0, and the induced electromotive force generated by the rod is less than BLv0, then the power of the resistor R between AB is less than B2L2v20R, so c is wrong;

D, according to the conservation of energy, when the rod reaches the extreme right for the first time, the mechanical energy of the object is completely converted into Joule heat in the whole loop, and the elastic potential energy of the springs A and B is equal, so the elastic potential energy of A is 12( 12mv20? 4Q)= 14mv20？ 2Q, so d is correct;

So I chose ABD.