a light spring whose unstretched length is 2.0 cm. You're going to use this spring to measure charge. First, you attach one end of the spring to the ceiling and hang a 1.0 g plastic ball from it. This stretches the spring to a length of 2.3 cm. You then give the plastic ball some charge. An electric field of 100 V m-1 is now applied, acting horizontally, and the spring both stretches and rotates to make an angle of 4o with respect to the vertical direction.
What is the charge on the ball?
What is the new length of the stretched spring once the electric field is applied?