Buggé/Fitzgerald: Kinematics 5
SPEEDS THEY ARE A CHANGING
5.1 The table below describes the velocity of a ball for different experiments. For each
experiment, something happens to the ball and its velocity changes. Use the information in table
to fill in the blanks in the table below.
5.2 A stoplight turns yellow when you are 20 m from the edge of the intersection. Your car is
traveling at 12 m/s; after you hit the brakes, the car's speed decreases at a rate of 6.0 m/s each
second. (Ignore the reaction time needed to bring your foot from the floor to the brake pedal).
a) Sketch the situation. Decide where the origin of the coordinate system is and what direction is
positive.
b) Draw a motion diagram.
c) Draw an x(t) graph.
d) Draw a v(t) graph.
e) Draw an a(t) graph
f) Write an expression for x(t) and v(t).
g) Use the expressions above to determine as many unknowns as you can.
Buggé/Fitzgerald: Kinematics 5
5.3 An object moves horizontally. The equations below represent its motion mathematically.
Describe the actual motion that these two equations together might describe.
v = +20 m/s + (−2 m/s2)t
x = −200 m + (+20 m/s)t + ½ (−2 m/s2 )t 2
a) Describe the motion in words and sketch the process represented in the two mathematical
expressions above. Act it out.
b) Draw a motion diagram
c) Draw a position-versus-clock reading graph and a velocity-versus-clock reading graph
d) Determine when and where the object will stop.
5.4 The data recorded in the table below are a record of the up and down motion of the center of
a ball thrown upward.
Clock Reading (s)
Position (m)
0.000
0.00
0.133
0.44
0.267
0.71
0.400
0.80
0.533
0.71
0.667
0.42
0.800
-0.04
a.
b.
c.
d.
Sketch a motion diagram for the ball modeled as a point object.
Draw a position vs. time graph
Draw a velocity vs time graph. Find its slope. What do we call this slope?
Use the velocity vs. time graph to determine the ball’s acceleration at the very top of its
trajectory.
e. What is the ball’s velocity at the top?
f. Can you reconcile these two answers? Explain.
g. Use the velocity vs. time graph to determine the distance that the ball traveled during the
trip from clock reading 0.000 to 0.800s.