toledo (gt4725) – hwk 1 – metaxas – (16111)
1
This
printout
should
have
18
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
Homework 1 is based on chapter 2. It is due
on Monday 1/31/11 at midnight and consists
of 10 questions.
It will say it is due at 2am
on Tuesday, but the computer is in Texas and
2am there is midnight of the previous day
here.
001(part1of2)10.0points
A runner is jogging at a steady 5
.
2 km
/
hr.
When the runner is 7
.
9 km from the finish
line, a bird begins flying from the runner to
the finish line at 15
.
6 km
/
hr (3 times as fast
as the runner).
When the bird reaches the
finish line, it turns around and flies back to
the runner.
L
v
b
v
r
finish
line
How far does the bird travel? Even though
the bird is a dodo, assume that it occupies
only one point in space (a “zero” length bird)
and that it can turn without loss of speed.
Correct answer: 11
.
85 km.
Explanation:
Let :
v
r
= 5
.
2 km
/
hr
,
L
= 7
.
9 km
,
and
v
b
= 3
v
r
.
finish
line
L
1
d
r
1
d
b
1
The runner travels a distance
x
until the
encounter with the bird. In that time, the bird
has traveled a distance
L
+(
L

x
) = 2
L

x .
The bird travel 3 times as fast as the runner
during this time frame, so
d
b
= 3
d
r
2
L

x
= 3
x
2
L
= 4
x
x
=
1
2
L
and the bird flies a distance of
d
b
= 2
L

1
2
L
=
3
2
L
=
3
2
(7
.
9 km)
=
11
.
85 km
.
002(part2of2)10.0points
After this first encounter, the bird then turns
around and flies from the runner back to the
finish line, turns around again and flies back
to the runner. The bird repeats the back and
forth trips until the runner reaches the finish
line.
How far does the bird travel from the be
ginning (including the distance traveled to the
first encounter)?
Correct answer: 23
.
7 km.
Explanation:
The distance remaining for the runner after
the first encounter is
L
1
=
1
2
L ,
and again the
bird will fly 3 times as far as the runner until
the next encounter. This pattern repeats over
the entire original distance, so
d
b
= 3
L
= 3 (7
.
9 km) =
23
.
7 km
.
003(part1of2)10.0points
A speedy tortoise can run at 0
.
08 m
/
s, and a
hare can run 19 times as fast. In a race, they
start at the same time, but the hare stops to
rest for 2
.
2 min, so the tortoise wins by a shell
(20 cm).
How long does the race take?
Correct answer: 139
.
194 s.
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toledo (gt4725) – hwk 1 – metaxas – (16111)
2
Explanation:
Let :
v
t
= 0
.
08 m
/
s
,
v
h
= 19
v
t
,
τ
= 2
.
2 min
,
and
Δ
ℓ
= 0
.
2 m
.
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 Spring '11
 Chiu
 Physics, Acceleration, Work, Velocity, Correct Answer, m/s, Toledo

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