Awaterwheel built in hamah, syria, has a radius of 20.0 m. if the tangential velocity at the wheel's edge is 7.85 m/s, what is the centripetal acceleration of the wheel?

We are tasked to solved for the centripetal acceleration given the radius and the tangetial velocity. USing the formula of Centripetal acceleration,

= 

Given:
= 7.85 m/s
r= 20.0 m

By Substitution,

= 
= 
= 
= 3.081125 m/

Therefore, the centripetal acceleration is 3.08 m/

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. 

Ray 2 should cross through the focal point on the right side of the lens