CH2H1 – florin – (56950)
1
This printout should have 29 questions.
Multiplechoice questions may continue on
the
next
column
or
page – find
all
choices before answering.
1
10.0 points
A
ball moves in the direction of the arrow labeled
c
in the following diagram. The ball is struck by a
stick that briefly exerts a force on the ball in the
direction of the arrow labeled
e
. Which arrow best
describes the direction
of
~p
, the change in the
ball’s momentum?
a
h
b
g
c
f
d
e
1. e correct
2. a
3. c
4. g
5. f
6. d
7. h
8. b
Explanation:
Recall the definition of impulse:
~
Impulse =
F
net
t
=
~p.
Therefore,
whatever
direction
the
net
force points in, that will be the direction
of the change in the ball’s momentum. We
are told that the force is in the direction
of
e
, so that is the correct answer.
002
10.0 points
You observe three carts moving to the
left. Cart A moves to the left at nearly
constant speed. Cart B moves to the left,
gradually speeding up. Cart C moves to the
left, gradually slowing down. Which cart
or carts, if any, experience a net force to
the left? Give all correct choices, with
your answers separated by commas.
A.
Cart A
B.
Cart B
C.
Cart C
D.
None
Correct answer:
B.
Explanation:
Keep in mind what is meant by “net force.”
The net force is the vector sum of all the
forces acting on an object. A net leftward
force would mean that all vertical (upward or
downward) forces cancel, and that the forces
acting toward the left are greater than those
acting toward the right. We also know that a
net force acting in some direction will cause an
acceleration in that direction.
Let’s examine each cart. Cart A is moving at
nearly constant speed. In this case, there
would be nearly zero net force acting on the
cart, since it is not accelerating in any direc
tion. So
A
is not a correct answer. Cart B
IS
accelerating toward the left, so it does appear
that there is a net leftward force acting here.
Finally, Cart C is slowing down as it moves to
the left, so in this case the net force is
actually to the right, since the acceleration is
in that direction. So
C
is not correct either,
meaning the only correct choice is
B
.
003 (part 1 of 3) 10.0 points
A hockey puck is sliding along the ice
with nearly constant momentum
~p
i
=
h
10
,
0
,
6
O
kg
·
m
/
s
when it is suddenly struck by a hockey
stick with a force
~
F
=
h
0
,
0
,
2000
O
N
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2
that lasts for only 7 milliseconds (0
.
007 s).
What is the final momentum
~p
f
of the puck?
Begin by finding just the
x
component,
p
f,x
.
Answer in kg
·
m
/
s.
Correct answer:
10 kg
·
m
/
s.
Explanation:
This is a straightforward application of the
momentum principle. Let the system be the
puck, and assume the only significant interac
tion on the system is with the hockey stick.
~
~p
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 Spring '08
 Turner
 Force, Momentum, Correct Answer, ~P

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