A small 13.0g plastic ball is tied to a very light 26.2cmstring that is attached
ID: 2284553 • Letter: A
Question
A small 13.0g plastic ball is tied to a very light 26.2cmstring that is attached to the vertical wall of a room. (See the figure (Figure 1) .) A uniform horizontal electric field exists in this room. When the ball has been given an excess charge of -1.10?C , you observe that it remains suspended, with the string making an angle of 17.4? with the wall.
A)Find the magnitude of the electric field in the room.
B) Find the direction of the electric field in the room. Pick one of the two
-to the left
or
-to the right
17.4°Explanation / Answer
a) sum forces in the y
T cos theta - mg = 0
so T = mg/cos(theta)
sum inthe x
q E - T sin theta = 0
q E = m g tan theta
E = m g tan theta/q = 13.0E-3*9.81*tan(17.4 degrees)/1.1E-6= 3.63E4 N/C
b) since we need force to go the right and charge is negative
E goes to the left