How do we ‘charge’ a pith ball? How do we ‘neutralize’ a pith ball?

How would you place two electrons on a sphere of radius r so that the electrostatic potential energy is minimized. how would you place three electrons to solve the same problem.

Refrigerant-134a flows through a carnot heat pump cycle at 0.5 kg/s. it is known that the maximum absolute temperature in the cycle is 1.1 times the minimum absolute temperature, and the net power input to the cycle is 2.5 kw. if the refrigerant changes from a saturated vapor to a saturated liquid during the heat rejection process, determine the maximum magnitude of the enthalpy of vaporization for this process in kj/kg (with 3 significant figures).

Abig box of sausages (30 kg) are lifted from the ground to the top shelf of the freezer. if the box is lifted at a constant speed, a distance of 1.75 m, what work is done by gravity?