일반물리학 2 — Magnetic Fields: Problem 13

13 A 0.85 kg copper rod rests on two horizontal rails 1.0 m apart and carries a current of 65 A from one rail to the other. The coefficient of static friction between rod and rails is 0.50. What are the (a) magnitude and (b) angle (relative to the vertical) of the smallest magnetic field that puts the rod on the verge of sliding?