Physics

Problem

A flat metal plate of mass

m

is released from rest at the upper edge of a uniform magnetic field. While within the field, the retarding force on the plate is proportional to its instantaneous speed,

F = k v

, where

k

is a constant. Ignoring air resistance, which expression gives the speed

v(t)

of the plate after time

t

? a)

\dfrac{mg}{k}\, e^{-(k/m) t}

\dfrac{mg}{k}\left(1+ e^{-(k/m) t}\right)

\dfrac{mg}{k}\left(1- e^{-(k/m)t}\right)

\dfrac{mg}{k}\left(1- e^{-(k/2m)t}\right)

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