Two swimmers, chris and sarah, start together at the same point on the bank of a wide stream that flows with a speed v. both move at the same speed c (where c > v) relative to the water. chris swims downstream a distance l and then upstream the same distance. sarah swims so that her motion relative to the earth is perpendicular to the banks of the stream. she swims the distance l and then back the same distance, with both swimmers returning to the starting point.
in terms of l c and v find the time intervals required
a) for chris's round trip and
b) for sarah's round trip.
c) explain which swimmer returns first.

Iam looking for this answer too!

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. 

The upward force acting on the wing of a airplane in flight is known as the "lift" force. (d)

Well it depends on the object or substance