Charging by Contact: Calculating Charge on a Sphere after Multiple Contacts

[9giddjl]

Electrostatics question, need help urgent!

Homework Statement

A small metal sphere carrying a charge of -2Q is first brought into contact with sphere R Which has a charge of +Q, and then into contact with sphere S which has a charge of +2Q, and finally into contact with sphere T which has a charge of +3Q. After making contact with the three spheres, in the stated order, the charge on the sphere at T is?

Homework Equations

F=kqQ/d^2

The Attempt at a Solution

Honestly, I've never learned how to do these sort of questions. I'd just like some insight on how to do these types of questions! any help is muchly appreciated ! please help, thankyou

 

[rl.bhat]

If the charged spheres are identical, the net charge will be shared equally by them. In the first case, after contact the net charge is -Q. So the charge on each sphere is - Q/2.
In similar way try the other cases.

 

[9giddjl]

Thank you. I understand how to do the question now. The answer is +15/8 Q.