Our high school student now has a question about potential energy due to gravity. she says, "i don't get the formula pe = mgh. it seems i can change the amount of potential energy something has just by changing my h = 0 point. say i'm holding a 3kg book over my head (two meters above my feet), but also say i'm on top of a 50 meter building. what's the potential energy of the book? is it mg2 (measuring from my feet) or is it mg52 (measuring from the ground)? "

You need to be more specific.  i really don't know what a "motion map" is.you can draw a graph of an object's position, distance, displacement, speed,velocity, or acceleration versus time, or you can draw a graph of the object's x-position versus its y-position and not give any information about time at all.if the graph presents position or displacement against time,  then constant velocity is a straight line . . i.e. a line that has  constant slope.if the graph shows speed against time, then constant velocityis a horizontal piece of line.if the graph shows acceleration against time, then constant  velocity is a piece of line that lies on the x-axis . . it's value is zero. 

Answerthe force between the charges will be  f/9 (one-ninth of force f)explanationcoulomb's law relates the magnitudes  two point charges q₁ and q₂, the distance, r, between the charges, and the electrostatic force, f, between the two charges:     k represents coulomb's constant, k = 8.99×10⁹ n·m²/c².note that if we have r = 3r, then