A large (infinite) rubber sheet which holds a charge per unit area of +s = +5 µC

Question

A large (infinite) rubber sheet which holds a charge per unit area of +s = +5 µC/m2 is oriented vertically. A small 12 gram plastic ball is tied to the end of a thread which is attached to the wall. You notice that the thread makes and angle of ? = 30 degrees with respect to the wall as shown in the figure. (HINT: First, draw a free body diagram for the mass showing all the forces on it.)
(a) Which is the magnitude and direction of the electric field at the position of the ball?
Magnitude N/C
direction
(b) What is the tension in the thread? N
(c) What is the charge on the ball? µC

Explanation / Answer

Please change your figures or let me know if you need further help

A large (infinite) rubber sheet which holds a charge per unit area of s = +1µC/m^2 is oriented vertically. A small 30 gram plastic ball is tied to the end of a thread which is attached to the wall. The thread makes a an angle of ? = 30 degrees with respect to the wall.

A) three forces. electric force go outward from the sheet, gravity force and tension of string.
B)Gauss's law.
s*S/epsilon0=E*2*S
so E=s/2epsilon0=56470(V/m)
C) tension T
we have
T*cos30=mg
so T=mg/cos30=0.34(N).
D) electric force.
Fe=T*sin30=0.17(N).
F=E*q
so q=F/E=3e-6(C)

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