CT2-1. A person starts in Boulder, drives to Denver, 50 km away, in 1 hour, stays in
Denver for 1 hour, then speeds back to Boulder in 30 minutes.
50 km in 1 hour
start
Denver
finish
.
(Wait 1 hour)
50 km in 1/2 hour
What is the average speed of this round trip?
A: zero
B: 67 km/hr
C: 40 km/hr
D: 75 km/hr
E: None of these.
What is the average velocity of this round trip? (same choices)
Answers: Average speed is (100 km) / (2.5 hr) = 40 km/hr
x
Average velocity = 0 since v 
and xfinal = xinitial  v = 0
t
CT2-2.A person initially at
point 3 on the x-axis stays there
for a little while and then strolls
along the x-axis to point 1, stays
there for a moment and then runs
to point 2 and remains there.
Which of the following graphs
correctly depicts this motion?
0
1
2
3
x
3
slow 1
fast
2
x
x
A
B
time
x
time
x
D
C
time
E: None of these!
Answer: D
time
CT2-3. A object starts at x = +5 and moves left along the x-axis at constant speed:
start
finish
x
0
Which graph represents this motion?
x
x
A
B
time
x
x
C
time
E: None of these!
Answer: B
time
D
time
CT2-4.A train car moves along a long straight track. The graph shows the position as a
function of time for the train.
position
time
The graph shows that the train:
A: speeds up all the time.
B: slows down all the time.
C: speeds up part of the time and slows down part of the time.
D: moves at constant velocity.
E: None of these statements is true.
Answer: B. The train is slowing down all the time because the slope of the curve is
always decreasing. On a graph of x vs. t , the slope is the velocity.
CT2-5. A train moves along a straight track and its position vs. time looks like:
x
t
Which graph best depicts the train's velocity vs. time?
v
v
A
B
t
v
v
C
Answer: D
t
t
D
t
CT2-6. The graph show positions
as a function of time for two trains
running on parallel tracks.
Which statement is true:
position
A: At time tC, both trains have the
same velocity.
B: Both trains speed up all the
time.
C: Both trains have the same velocity at some time before tC.
D: At some time, both trains have the same acceleration.
E: None of the above statements is true.
train A
train B
tC
time
Answer: B: Both trains have the same velocity when the slopes of the two curves are
equal. Notice that train A has constant velocity and therefore has zero acceleration. Train
B is slowing down all the time. Train B has negative velocity.
CT2-7. An object's velocity vs. time is:
v
t
Which graph best represents the object's acceleration vs. time?
a
a
A
B
t
a
t
a
C
t
Answer: D. The slope of a curve of v vs. t is the acceleration a.
D
t
CT2-8. At the moment that the velocity is zero, what is the sign of the acceleration?
A) Positive B) negative C) zero
v
a=?
t
Is the acceleration constant all during the time the velocity is changing?
A) Yes, a = constant B) No, a is changing.
Answers: A) the acceleration is negative at the moment when the velocity is zero. A) the
acceleration is constant. The slope of a graph of v vs. t is the acceleration. Although v =
0 at an instant of time, the velocity is in the process of changing from positive v to
negative v.
CT2-9.
C
B
A
A glider on a tilted air track is given a brief push uphill. The glider coasts up to near the
top end, stops, and then slides back down. When the glider is at the highest point of its
path, its acceleration is..
A: straight down
C: upward along the track
B: downward along the track
D: no direction, the acceleration is zero.
Answer: B. the direction of "Delta-v" is downward along the track. Just before the glider
reaches the top, the velocity v1 is upward along the track. Just after the glider reaches the
top, the velocity v2 is downward along the track. The change in velocity v is the vector
that changes v1 into v2. The direction of the acceleration is the same as the direction of
v.
v2
2
v1
v
CT2-10. A ball is thrown straight upward. At the top of its trajectory, its acceleration is..
A:
B:
C:
D:
zero
straight up
straight down
depends on the mass of the ball
CT2-11. If you drop an object in the absence of air resistance, it accelerates downward at
9.8m/s2. If instead you throw it downward, its downward acceleration after release is….
A: less than 9.8m/s2.
B: 9.8m/s2
C: more than 9.8m/s2.
CT2-12..An object's velocity vs. time graph looks like this:
v
t
What situation produces this kind of motion?
A) A rock is thrown straight up.
B) A rock is dropped from rest.
C) A rock is thrown straight down.
D) A book slides along a table and comes to rest
E) None of these.
CT2-13. On planet X, a cannon ball is fired straight upward. The position and velocity of
the ball at many times are listed below. Note that we have chosen up as the positive
direction.
Time(s)
0
1
2
3
4
5
6
7
8
Height(m)
0
17.5
30
37.5
40
37.5
30
17.5
0
Velocity(m/s)
20
15
10
5
0
-5
-10
-15
-20
y
What is the acceleration due to gravity on Planet X?
A: -5m/s2
D: -20m/s2
B: -10m/s2
E: None of these.
C: -15m/s2
CT2-14. A ball is fired straight downward out of a special spring-loaded gun, which
produces constant acceleration. Upward is chosen as the positive direction. Assume that
air resistance is negligible. Which graph properly represents acceleration of the ball?
a
Ball released
From spring
t
A
a
t
B
a
t
C
D: None of these
CT2-15.
A truck traveling at 50 km/hr approaches a car stopped at a red light. When the truck is
100m from the back of the car, the light turns green and the car immediately begins to
accelerate at 2.00m/s2. Which graph belows represents this situation?
car
A
x
B
t
truck
C
x
car
t
truck
x
car
D: None of these
t
truck
CT2-15
A ball is fired from a canon straight upward with an initial velocity vo. Assume no air
resistance. If the initial velocity vo is doubled, the time to reach the apex of the
trajectory..
A: doubles.
B: increases by a factor of 4.
C: Neither of these.
D: Impossible to tell from the information given.
If the initial velocity vo is doubled, the maximum height of the ball..
A: doubles.
B: increases by a factor of 4.
C: Neither of these.
D: Impossible to tell from the information given.
CT2-17
The distance x traveled by a ball in a time t is given by the formula
x
1
a t2
2
where a is a non-zero positive constant. What happens to the distance x when the time t
is tripled?
A) x increases by a factor of 3
B) x increases by a factor of 9/2
C) x increases by a factor of 9
D) x increases by a factor that depends on the value of a
Do you have your clicker with you today?
A) Yes
B) No
A trick question:
Which object, A or B, has larger velocity?
A: A
v
A
B
t
A better question:
Which object, A or B, has higher speed? A: B:
B: B