Key to Magnets Part 1 gizmo?

A100-watt light bulb illuminates a solar cell. the electricity from the solar cell operates a water pump that delivers 1 watt of power. what is the efficiency of the system?

What is the orbital period of a spacecraft in a low orbit near the surface of mars? the radius of mars is 3.4×106m.

How does the electric potential energy between two charged particles change if one particle is reduced by a factor of 3? a. increased by a factor of 3 b. it is decreased by a factor of 9 c. it is reduced by a factor of 3 d. it is increased by a factor of 9