An uncharged parallel-plate capacitor is connected through an open switch to a battery of voltage VV. The switch is closed and the capacitor is allowed to charge. As the capacitor is charged, energy is transferred to it from the battery. When the capacitor is fully charged, the energy stored in the capacitor is U1U1 . The energy stored in the capacitor when the stored charge is q02q02 is

(1/2)U₁

Explanation:

An uncharged parallel-plate capacitor is connected through an open switch to a battery of voltage VV. The switch is closed and the capacitor is allowed to charge. As the capacitor is charged, energy is transferred to it from the battery. When the capacitor is fully charged, the energy stored in the capacitor is U1U1 . The energy stored in the capacitor when the stored charge is q₁/2 is

Solution:

A capacitor is an electrical device used to store electrical energy in an electric field. The energy stored in a capacitor is given by:

U = (1/2)QV; where U is the energy stored, Q is the charge and V is the voltage applied.

The energy stored in a fully charged capacitor with a charge q₁ and battery of voltage V is given as:

U₁ = (1/2)q₁V

If the stored charge is q₁/2, the energy stored (U₂) becomes:

U₂ = (1/2)(q₁ / 2)V

U₂ = (1/2)*  (1/2)q₁V

U₂ = (1/2)U₁

there are no contact forces mentioned on the list of choices that you've provided.