What is the Charge on a Bead Accelerating in a Uniform Electric Field?

[Sarah88]

Homework Statement

A small charged bead has a mass of 1.0 g. It is held in a uniform electric field E= 200,000 N/C up. When the bead is released, it accelerates upward with an acceleration of 20 m/s^2. What is the charge on the bead?

Homework Equations

F= qE
F= mg
(possibly F= ma)

The Attempt at a Solution

I tried this problem multiple different ways including:
mg-Eq= 0
as well as Eq= ma

However, I wasn't sure how to relate the three force equations (mg, ma, Eq) together for this problem (because all seem relevant in this problem). Thank you!

 

[tiny-tim]

Welcome to PF!

Hi Sarah! Welcome to PF!

I tried this problem multiple different ways including:
mg-Eq= 0
as well as Eq= ma

However, I wasn't sure how to relate the three force equations (mg, ma, Eq) together for this problem (because all seem relevant in this problem). Thank you!

Well, you're nearly there …

as in almost all dynamics problems, just apply good ol' Newton's second law …

sum of forces = mass times acceleration …

what do you get? ​

 

[Sarah88]

Hi,
Thanks for the welcome to the forum :)

Well, the sum of forces equal to ma: Eq- mg (oppose each-other) = ma, it makes a lot more sense when you take into account Newton's second law. Thank you for your help! :)