1. The problem statement, all variables and given/known data As shown in the figure above, a ball of mass 0.720 g and positive charge q =39.4microC is suspended on a string of negligible mass in a uniform electric field. We observe that the ball hangs at an angle of theta=15.0o from the vertical. What is the magnitude of the electric field? (The figure shows the ball hanging 15 degrees to the left of the y-axis, and the electric field points to the left) 2. Relevant equations F = ma E = F/q Sum of forces = 0 Sum of forces = tension + e-field - weight = 0 3. The attempt at a solution I drew a free-body diagram, and found the forces due to the tension and weight to be F = mg*cos(15) or F = 6.816 Then I used E = F/q, to get 1.73*10^5 N/C I think I'm missing a step? Or calculating the force incorrectly? Thank you!