100. (a) We apply Newton’s second law to the rod
mdv
dt =iBL ,
and integrate to obtain
v=iBLt
m.
The velocity v points away from the generator G.
(b) When the current iin the rod becomes zero, the ro d will no longer be accelerated by a force
F=iBL and will therefore reach a constant terminal velocity. This occurs when |Einduced|=E.
Specifically,
|Einduced|=
dΦB
dt
=
d(BA)
dt
=B
dA
dt
=BvL =E.
Thus, v =E/BL,leftward.
(c) In case (a) electric energy is supplied by the generator and is transferred into the kinetic energy
of the rod. In the case considered now the battery initially supplies electric energy to the rod,
causing its kinetic energy to increase to a maximum value of 1
2mv2=1
2(E/BL)2. Afterwards, there
is no further energy transfer from the battery to the rod, and the kinetic energy of the rod remains
constant.
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