Can somebody me with physics : )

number 36

Four objects each with charge +2.0×10−7c are located at the corners of a square whose sides are 2.0 m long. part a what quantities can be determined using this information? check all that apply. the electric force on a charged object placed at the center of the square. the mass of each object. the total electric potential energy of the system consisting of the four charged objects. part b find the electric force on a charged object placed at the center of the square.

Four identical lab carts each have a mass of 200 kg. different masses are added to the carts and the velocities are measured. all carts move to the right.

Which stable element is used to determine the age of volcanic rock? a- argon b- carbon-14 c- potassium d- carbon-12