How do objects with the same charge ineract

Ihave a density of 1.61g/cm^3 and a mass of 28g. find the missing value

The diagram shows four locations in the electric field of a positive point charge m. at which location is the electric potential the greatest.

Consider a 1000 w iron whose base plate is made of 0.5 cm thick aluminum alloy 2024-t6 (ρ = 2770 kg/m3 and cp = 875 j/kg°c). the base plate has a surface area of 0.03 m2. initially, the iron is in thermal equilibrium with the ambient air at 22°c. assuming 90% of the heat generated in the resistance wires is transferred to the plate, determine the minimum time needed for the plate temperature to reach 200°c.