Answer
given,
mass of copper rod = 1 kg
horizontal rails = 1 m
Current (I) = 50 A
coefficient of static friction = 0.6
 magnetic force acting on a current carrying wire is
            F = B i L
Rod is not necessarily vertical


the normal reaction N = mg-F y
static friction       f = μ_s (mg-F y )
 horizontal acceleration is zero


  B_w = B sinθ
  B_d = B cosθ
iLB cosθ= μ_s (mg- iLB sinθ)





        B = 0.1 T