Question

describing motion with velocity - time graphs
read from lesson 4 of the 1 - d kinematics chapter at the physics classroom
http://www.physicsclassroom.com/class/1dkin/u1l4a.html
http://www.physicsclassroom.com/class/1dkin/u1l4b.html
http://www.physicsclassroom.com/class/1dkin/u1l4c.html
http://www.physicsclassroom.com/class/1dkin/u1l4d.html
mop connection: kinematic graphing: sublevels 5 - 8 (and some of sublevels 9 - 11)
motion can be described using words, diagrams, numerical information, equations, and graphs. describing motion with graphs involves representing how a quantity such as the objects velocity changes with respect to the time. the key to using velocity - time graphs is knowing that the slope of a velocity - time graph represents the objects acceleration and the area represents the displacement.
review:

1. categorize the following motions as being either examples of + or - acceleration.

a. moving in the + direction and speeding up (getting faster)
b. moving in the + direction and slowing down (getting slower)
c. moving in the - direction and speeding up (getting faster)
d. moving in the - direction and slowing down (getting slower)
interpreting velocity - graphs

1. on the graphs below, draw two lines/curves to represent the given verbal descriptions; label the lines/curves as a or b.

a moving at constant speed in - direction
b moving at constant speed in + direction
a moving in + direction and speeding up
b moving in - direction and speeding up
a moving in + direction and slowing down
b moving in - direction and slowing down
a moving with + velocity and - acceln
b moving with + velocity and + acceln
a moving with - velocity and - acceln
b moving with - velocity and + acceln
a moving in + dirn, first fast, then slow
b moving in - dirn, first fast, then slow

Explanation:

Step1: Recall acceleration - velocity relationship

Acceleration is the rate of change of velocity. If velocity and acceleration have the same sign, speed increases; if opposite, speed decreases.

Step2: Analyze case a

Moving in + direction and speeding up means velocity and acceleration are both positive. So it's + acceleration.

Step3: Analyze case b

Moving in + direction and slowing down means velocity is positive and acceleration is negative. So it's - acceleration.

Step4: Analyze case c

Moving in - direction and speeding up means velocity and acceleration are both negative. So it's - acceleration.

Step5: Analyze case d

Moving in - direction and slowing down means velocity is negative and acceleration is positive. So it's + acceleration.

Answer:

a. + acceleration
b. - acceleration
c. - acceleration
d. + acceleration