Consider the following combinations of signs and values for velocity and acceleration of a particle with respect to a one-dimensional x axis:
Velocity Acceleration
a. Positive Positive
b. Positive Negative
c. Positive Zero
d. Negative Positive
e. Negative Negative
f. Negative Zero
g. Zero Positive
h. Zero Negative
Describe what a particle is doing in each case, and give a real life example for an automobile on an east-west one-dimensional axis, with east considered the positive direction.