Question

Which of the following five position versus time graphs represents the motion of an object moving with a constant nonzero speed?

Answer 1

first choose two point on every graph.then v(avg)=y2-y1/x2-x1

Answer 2

How would I do this without a numerical value for time? How do I determine what two points to choose.

Answer 3

Have you already studied the equation y = mx + q? It's the equation of the straight line, while, for instance, y = ax^2 +bx + c is the equation of the parabola.
When a body moves with constant velocity, it has the equation y = vx + q, where x is time, v is the constant velocity and q is the starting point. Is it more clear what are the correct graphs?
(if you have alreay studied derivatives, remember that velocity is position's time derivative, so if velocity is constant, position is a straight line)
SPOILER ALERT

The correct graphs are the ones with a straight line.

Answer 4

Andrea therefore if it is a straight line than it would be B? because I would think that the other graphs dont apply because it looks like the other graphs represent a object that is either at rest, or not having a constant speed.

Answer 5

An object at rest has constant velocity v = 0.
If an object has a position function x(t) and it's derivative (velocity, v(t) ) is constant, then (as a consequence of Lagrange theorem for real functions) its graph is a straight line. This is true also if velocity is constant and equals to 0.