Can someone help me with these Physics problems?

Question

matt101 · Answer

From Coulomb's Law, you can find the charge on the sphere using:

$$E={kq \over r^2}$$
What do you get for #1?

anonymous · Answer

That's what I got

matt101 · Answer

I agree with you that the magnitude of the charge is what you got, 3 x 10^(-9) C.

But is the charge positive or negative? Keep in mind the electric field is pointing TOWARDS the sphere.

anonymous · Answer

I am not too sure.  If i had to guess maybe positive?

matt101 · Answer

By convention, the electric field points in the direction a positive test charge would travel. If the electric field points towards the sphere, a positive charge would travel towards the sphere. If the positive charge is attracted to the sphere, what is the charge of the sphere?

anonymous · Answer

Negative? because our answer had a negative exponent in it

matt101 · Answer

Well the fact that the exponent is negative doesn't necessarily mean the charge itself is negative. The negative exponent just means the size of the charge is very small.

The charge is negative though, because if a positive charge is attracted towards the sphere, the sphere must be negative (opposites attract).

Does that make sense?

matt101 · Answer

Yes that's right!

anonymous · Answer

Alright thank you.  Im going to post the other questions on a different post, so I can reward you more medals.  :)