Ahall-effect probe operates with a 120 -ma current. when the probe is placed in a uniform magnetic field of magnitude 0.0740 t, it produces a hall voltage of 0.620 µv.
(a) when it is used to measure an unknown magnetic field, the hall voltage is 0.400 µv. what is the magnitude of the unknown field?
mt
(b) the thickness of the probe in the direction of b is 2.00 mm. find the density of the charge carriers, each of which has charge of magnitude e).
m-3

Sorry i don’t know what to do

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. 

They like garbage and they hunt during the night.