Question

12.

a. You do 31 J of work to move a -15 uC from infinity to a spot some distance away from a -11 uC charge. What is that distance? [4.8 cm]

b. The work you did is stored as potential energy in the system as long as the charges are both held fixed in that position. You then let the -15 uC charge go. If that point charge has a mass of 7.2x10-12 kg, how fast will it be going once it is very far away (approximate as infinity) from the other charge? [2.9x106 m/s]

Answer 1

Potential Energy is calculated by following formula :

where, k = 9 x 10⁹ Nm²/C² ; q₁ , q₂   = magnitude of charges ; r = distance between them

In this case, work done will be stores as potential energy of the system, so,

Distance = 4.8 cm

In this case all stored energy will be converted to kinetic energy of -15 microcoulomb charge.

So,

Velocity = 2.9 x 10⁶ m/s