An insulating rod having linear charge density `lambda = 40.0 mu Cm^-1` and linear mass density `mu = 0.100 kg m^-1` is released from rest in a uniform electric field `E = 100 Vm^(-1)` directed perpendicular to the rod.
(a) Determine the speed of the rod after it has travelled 2.00 m
(b) How does your answer to part (a) change if the electric field is not perpendicular to the rod ?

Explanation

Arbitrarily take `V = 0` at the initial point. Then at distance d downfield, where L is the rod length,
`V = -E d` and `U_e = lambda L E d`
a. `(K + U)_i = (K + U)_f`
or `0 + 0 = (1)/(2) mu L v^2 - lambda L E d`
or `v = sqrt((2 lambda E d)/mu) = 0.400 ms^(-1)`
b. The same.