(1) There must be qE=mg because both charged balls are moving in a uniform circular motion in the composite field.

It can be seen from the direction of the electric field that both balls are negatively charged. ...

mAg=qAE…②

mBg=qBE…③

mA=3mB，

So qaqb = 3 1...④

(2) According to the meaning of the question, the two charged balls are in the same direction ...

By qBv=mv2R

Have to? R=mvqB…⑥

From the meaning of the question, RA=3RB,

So vavb = 3 1...⑦

(3) Because two charged balls collide at P, the tangential force is zero, so the tangential momentum of the two charged balls at P is conserved.

By mAvA+mBvB=mv'A+mv'B…⑧

Get v 'a = 73vb ... pet-name ruby.

RAR’A = mAv’AqABmAvAqAB = v’AvA = 73v’B3vB = 79…

So r 'a = 79ra = 7cm ... (11)

Answer: (1) Try to explain what charges balls A and B carry, and the ratio of their charges qAqB is equal to 3;

(2) Ball A and Ball B hover in the same direction, and the size ratio is 3;

(3) If charged balls A and B collide at the position P shown in the figure, and charged ball B, which originally moved in a small circular orbit after collision, can just move along a large circular orbit, then the orbital radius of the circular motion of charged ball A after collision is 7 cm.