schneiter (tcs639) – HW04 – Ross – (89152)
1
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10
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001
(part 1 of 3) 10.0 points
Two canoeists in identical canoes exert the
same effort paddling and hence maintain the
same speed relative to the water.
One pad
dles directly upstream (and moves upstream),
whereas
the
other paddles
directly down
stream.
With downstream as the positive
direction, an observer on shore determines the
velocities of the two canoes to be

1
.
5 m
/
s
and 2
.
7 m
/
s, respectively.
What is the speed of the water relative to
shore?
Correct answer: 0
.
6 m
/
s.
Explanation:
Let
v
1
s
= velocity of canoe1 relative to shore,
v
2
s
= velocity of canoe2 relative to shore,
v
1
w
= velocity of canoe1 relative to water,
v
2
w
= velocity of canoe2 relative to water,
and
v
ws
= velocity of water relative to shore.
Given :
v
1
s
=

1
.
5 m
/
s
,
v
2
s
= 2
.
7 m
/
s
,
and
v
1
w
=
v
2
w
.
v
cs
=
v
cw
+
v
ws
For the first canoe (moving upstream)
v
1
s
=
v
ws

v
1
w
For the second canoe (moving downstream)
v
2
s
=
v
ws
+
v
2
w
adding these equations
v
1
s
+
v
2
s
= 2
v
ws
since
v
1
w
=
v
2
w
.
Thus
v
ws
=
v
1
s
+
v
2
s
2
=

1
.
5 m
/
s + 2
.
7 m
/
s
2
=
0
.
6 m
/
s
.
002
(part 2 of 3) 10.0 points
What is the speed of the first canoe relative
to the water?
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 Spring '08
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 mechanics, Acceleration, Velocity, m/s, vy

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