A book sits on a desk that is 1 meter (m) high. The books gravitational potential energy is 10 joules (j). If the book falls from the desk, what is the sum, in joules, of its gravitational potential energy and kinetic energy when the book is 0.5m off the ground?(A)5 (B)10 (C)15 (D)20

the total distance that martina travels that day is

(distance from home to mom's office) plus (distance from mom's office to school)

plus (distance from school to library) plus (distance from library to friend's house)

plus (distance from friend's house to martina's house).

(we don't know what any of these distance actually is.)

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.