A 1 kg rock is sitting at the edge of a cliff 100 meters high. What is the rock's gravitational potential energy?

Will you chech and finish these for me, because i am stumped with them.

The man of mass m1 and the woman of mass m2 are standing on opposite ends of the platform of mass m0 which moves with negligible friction and is initially at rest with s = 0. the man and woman begin to approach each other. derive an expression for the displacement s of the platform when the two meet in terms of the displacement x1 of the man relative to the platform.

Does current flow through or across a resistor?