phy-electromagnetism

(a) Constant induced emf indicates that the rod is moving at a constant speed. As such, no net force is required according to Newton's First Law. Hence, the force is zero.
(b) Induced emf E = BLv
where B is the magnetic flux density
L is th elength of the rod
v is the speed of the rod

hence, differentiating both sides with respect ot t,
dE/dt = B.L(dv/dt)
dv/dt = (1/BL).(dE/dt) = 1/(0.4x0.2) m/s2 = 12.5 m/s2
But dv/dt is the acceleration of the rod
thus, force required = 0.1 x 12.5 N = 1.25 N