Why is resistivity needed to find heat from colliding charged spheres?

[LAph]

In free space there are two masses:
- Metallic sphere of mass M, radius R and total charge equal to 0. It has also a resistivityρ.
- Metallic sphere of mass m, radius r and charge q.
The distance between the masses is D. We can assume r <<R<<D and m<<M. The masses start accelerating until they collide anelasticaly. Find the energy that has become heat.

My question is: Why do I need ρ to solve this problem?
My solution is basically finding the difference between the initial potential energy and the final, but i haven't used the resistivity.

 

[berkeman]

In free space there are two masses:
- Metallic sphere of mass M, radius R and total charge equal to 0. It has also a resistivityρ.
- Metallic sphere of mass m, radius r and charge q.
The distance between the masses is D. We can assume r <<R<<D and m<<M. The masses start accelerating until they collide anelasticaly. Find the energy that has become heat.

My question is: Why do I need ρ to solve this problem?
My solution is basically finding the difference between the initial potential energy and the final, but i haven't used the resistivity.

Welcome to the PF.

You probably need the resistivity of the first sphere because currents will likely flow as part of this process.

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