homework 02 – ANDERSON, ZACH – Due: Sep 8 2007, 4:00 am
1
Question 1, chap 2, sect 6.
part 1 of 1
10 points
An object was suspended in a fixed place
(
y
= 0) and then allowed to drop in a free fall.
Taking up as the positive vertical direction,
which of the following graphs correctly repre
sents its vertical motion as
displacement
vs
time
?
1.
t
y
correct
2.
t
y
3.
t
y
4.
t
y
5.
t
y
6.
t
y
7.
t
y
8.
t
y
9.
t
y
10.
t
y
Explanation:
The object is undergoing a constant down
ward gravitational acceleration
g
. The slope
of a
position
vs
time
curve represents the
velocity. Given
g
negationslash
= 0 m
/
s
2
a <
0 m
/
s
2
a
=
−
g
m
/
s
2
v
0
= 0 m
/
s
y
0
= 0 m
.
Since
y
=
y
0
+
v
0
t
+
1
2
a t
2
,
therefore
y
=
−
1
2
g t
2
.
This is a parabolic shaped curve starting a
y
= 0 with a continuously decreasing slope
as time increases.
Only the figure below is
correct.
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homework 02 – ANDERSON, ZACH – Due: Sep 8 2007, 4:00 am
2
t
y
Question 2, chap 2, sect 1.
part 1 of 2
10 points
A student wanted to drive from Austin to
San Antonio, 80 miles south of Austin on
highway I35.
Unfortunately, he entered the
highway in the wrong direction and drove all
the way to Waco — 100 miles north of Austin
— before he noticed his error.
In Waco,
he turned around, drove back to Austin and
continued to San Antonio.
The whole trip
took 6
.
7 hours.
What was the student’s average speed dur
ing this trip?
Correct answer: 41
.
791 MPH (tolerance
±
1
%).
Explanation:
Basic Concept
:
(average speed) =
(total distance traveled)
time
The total distance traveled by the student
is 100 miles from Austin to Waco, plus an
other 100 miles from Waco back to Austin,
plus 80 miles from Austin to San Antonio,
or 280 miles altogether.
His average speed
therefore is

v

=
L
t
=
280 miles
6
.
7 hours
= 41
.
791 MPH
Question 3, chap 2, sect 1.
part 2 of 2
10 points
What was the student’s average velocity
during his trip? Take your positive direction
to be southbound on I35.
Correct answer: 11
.
9403
MPH (tolerance
±
1 %).
Explanation:
Basic Concept
:
(average velocity) =
(net displacement)
time
The student’s net displacement is from Austin
to San Antonio — the fact that he went their
by way of Waco is irrelevant for this question
— or 80 miles in the positive southbound
direction. His average velocity is therefore
v
=
Δ
X
t
=
80 miles
6
.
7 hours
= 11
.
9403 MPH
Question 4, chap 4, sect 4.
part 1 of 3
10 points
A boy is standing on a cliff.
The boy’s
hands are a height
b
above the ground level at
the base of the cliff.. A monkey is in a tree.
The monkey is at a height
h
above the boy’s
hands.
At
t
= 0 the boy throws a coconut
upward at a speed
v
0
, and at the same time
the monkey releases his grip, falling downward
to catch the coconut.
Assume the initial speed of the monkey is 0
m/s, and the cliff is high enough so that the
monkey is able to catch the coconut before
hitting the ground.
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 Fall '08
 Turner
 Acceleration, Work, Velocity, Correct Answer, m/s, ZACH

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