Formula to find mass of an object

Which simple machine is not part of this compound machine? a. lever b. pulley c. inclined plane d. wheel and axle

The table below shows the acceleration of gravity on different bodies in the solar system. on which body would a 10 kg lamp has the most gravitational potential energy when lifted to a height of 2 m? a. earth b. mars c. neptune d. uranus

Explain why electric current cannot exist if a current doesn't have a voltage source.