Make sure you use the Problem Solving Strategy for the problems below.
12.4 Practice A bus leaves an intersection accelerating at +2.0 m/s2 from rest (think what the term rest means).
Where is the bus after 5.0 s? Draw a motion diagram for this motion.
12.5 Practice A bicyclist slowed down from 8 m/s to 2 m/s in 3 seconds. What was the acceleration of the
bicycle? How far did it move during this process? Draw a motion diagram for this process.
12.6 Reason
The motion of a car can be described by the following function. All quantities are in SI units
x(t) =14t + 3t2
Explain the meaning of each number.
14 means:
3 means:
Describe the motion in words, with a motion diagram, and with a picture with a reference frame.
a) What would the v(t) expression look like?
b) Determine the position and the velocity of the car after 5 seconds.
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Homework
12.9 Represent and Reason
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. & Draw a v(t) graph
12
12
10
10
8
8
6
6
4
4
2
2
0
1
2
3
0
1
2
3
d) Write an expression for x(t) and v(t).
e) Use the expressions above to determine as many unknowns as you can.
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EXTRA PRACTICE ONLY!!!!!!!!
beyond this point….
12.10 Represent and Reason
A bus moving at 26 m/s (t = 0) slows at rate of 3.5 m/s each second. Sketch the situation. Decide where the
origin of the coordinate system is and what direction is positive.
a) Draw a motion diagram.
b) Use the expressions derived in this lesson and previous lessons to determine as many unknowns as you
can.
12.11 Reason and Represent
An object moves horizontally. The equations below represent its motion mathematically. Describe the actual
motion that these two equations together might describe.
a. v  20 m/s  (2 m/s2 )t
1
b. x  200 m  (20 m/s)t  (2 m/s 2 )t 2
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.
12.12 Reason and Represent
A remote control car runs down a driveway at an initial speed of 6.0 m/s for 8.0 sec, then uniformly increases its
speed to 9.75 m/s in 5.0 sec.
a) Sketch the situation, label all knowns and unknowns. Decide where the origin of the coordinate system
is and what direction is positive.
b) Draw a motion diagram.
c) Draw a v(t) graph.
d) Use the expressions in this and previous lessons to determine as many unknowns as you can.
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12.13 Regular problem
Examine the graph below.
a) Describe a real life situation that this graph could represent, be sure to include all the information on the graph
and any extra in your situation.
b) Determine two unknown physical quantities (one of them should be in the units of meters).
c) If the object was moving at a constant speed equal to the speed of the object on the graph at t = 0, what would
be the distance it traveled in 6 seconds? How does it compare to the distance the object on the graph traveled in
the same time interval? Does the answer make sense to you?
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