A small sphere has charge q $=+9\mathrm{.}0\backslash$mu C and mass m $=35$ g$.$

It is hung from a vertical spring, which causes the spring to

stretch by $$x $=7\mathrm{.}0$ cm from its equilibrium length. Then a

downward electric field is applied to this region of space, which

causes the sphere to descend through a distance of d $=2\mathrm{.}5$ cm$.$

What is the magnitude E of this electric field? For the limit

check, investigate what happens to E if the sphere barely re$-$

sponds to the electric field being turned on $($i$.$e$.,$ d $->0).$