PHYSICS QUESTION!!! PLEASE HELP!!!?

Question

A spherical water drop 1.60μ m in diameter is suspended in calm air owing to a downward-directed atmospheric electric field E = 472 N/C.

What is the weight of the drop?

How many excess electrons does it have?

Answer 1

for the drop to be suspended, the total force acting on it must be zero; this means that the weight down must be countered exactly by the electrical force up

to calculate the weight down, calculate the mass of the drop knowing that that m= density x volume, and the volume of a sphere is 4/3 pi r^3, where r is the radius of the sphere.

weight = mg where g is the acceleration due to gravity

then, this must be equal to the upward directed electric force, which is:

F=qE

knowing that qE=mg (and knowing E, m and g) you can solve for q, the net charge of the sphere

knowing the charge of 1 electron (which if memory serves me correctly is 1.6x10^(-19) C), you can divide your value of q by this factor and get the total number of charges

hope this helps