Ch2 HW2 2008 (Homework)
Arthur Barfield
PHYS 2211, section M, Fall 2008
Instructor: Jennifer Curtis
Web
Assign
Current Score:
21 out of 24.5
Due:
Friday, August 29, 2008 09:00 AM EDT
Description
Updating position if momentum is changing; Constant force; Graphs of motion
Instructions
Reading: Sec 2.42.5
Because problems 2 and 5 require a long chain of calculations, six submissions are permitted
for these problems. For problem 1 (multiple choice), only two submissions are permitted.
The due date for this assignment is past.
Your work can be viewed below, but no changes
can be made.
1. [MI2 02.RQ.16]
1/1 points
The x component of the momentum of an object is observed to increase with time:
At
t
= 0 s,
= 30 kg
·
m/s
At
t
= 1 s,
= 40 kg
·
m/s
At
t
= 2 s,
= 50 kg
·
m/s
At
t
= 3 s,
= 60 kg
·
m/s
What can you conclude about the x component of the net force acting on the object
during this time?
is zero.
Not enough information is given.
is decreasing with time.
is constant.
is increasing with time.
Solution or Explanation
The change in momentum is the same over every time interval.
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2. [MI2 02.P.26]
3/4.5 points
A pingpong ball whose mass is
0.0027
kg (
2.7
g) is acted upon by the Earth and the air (there
is air resistance, and there is also a strong wind). This table gives the position of the ball at
several times:
Time
Position
12.35
s
<
3.17
,
2.54
,
9.38
> m
12.39
s
<
3.25
,
2.50
,
9.40
> m
...
...
14.35
s
<
9.37
,
0.66
,
10.40
> m
14.39
s
<
9.54
,
0.75
,
10.42
> m
What was the average momentum of the ball during the earlier time interval, from
t
=
12.35
s to
12.39
s?
= <
.0054
0.0054
,
.0027
0.0027
,
.00135
0.00135
>
kg
·
m/s
What was the average momentum of the ball during the later time interval, from
t
=
14.35
s to
14.39
s?
= <
.01145
0.0115
,
.0061
0.00607
,
.00135
0.00135
> kg
·
m/s
In the time interval from
12.35
s to
14.35
s, what was the average net force acting on
the ball?
= <
(No Response)
0.00304
,
(No Response)
0.00169
,
(No
Response)
0
> N
Solution or Explanation
Apply the Momentum Principle to find the average net force.
3. [MI2 02.X.07.01]
2/2 points
(a) A runner starts from rest and in
3
s reaches a speed of
9
m/s. If we assume that the speed
changed at a constant rate (constant net force), what was the average speed during this
3
s
interval?
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 Spring '09
 Kindermann
 Current, Force, Momentum, Work, Velocity, ball, net force, Arthur Barfield PHYS

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