homework 08 – BAUTISTA, ALDO – Due: Feb 8 2006, 4:00 am
1
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Question 1
Part 1 of 2.
10 points.
Three
objects
can
only
move
along
a
straight, level path. The graphs below show
the position
d
of each of the objects plotted
as a function of time
t
.
d
t
I
d
t
II
d
t
III
The magnitude of the velocity
k
~v
k
of the
object increases in which of the cases?
1.
I, II, and III
2.
II and III only
3.
III only
correct
4.
I and III only
5.
I only
6.
I and II only
7.
II only
Explanation:
Case I: The object moves at constant speed.
Case II: The object remains at rest.
Case III: The speed of the object increases
with time;
i.e.
, constant acceleration.
Thus, the magnitude of the velocity of the
object increases only in case III.
Question 2
Part 2 of 2.
10 points.
The sum of the forces
X
F
i
= 0 on the
object is zero in which of the cases?
1.
I and II only
correct
2.
I only
3.
III only
4.
I, II, and III
5.
II and III only
6.
II only
7.
I and III only
Explanation:
When the sum of forces on the object is
zero, the acceleration of object is zero by
Newton’s 2nd law.
In cases I and II, the velocity of the object
doesn’t change with the time, so the sum of
the forces on the object is zero.
In case III, the object is accelerating, so the
sum of forces on the object is not zero.
Question 3
Part 1 of 1.
10 points.
A block of mass
m
accelerates with acceler
ation
g
up a frictionless plane that is inclined
at an angle
α
above the horizontal. The force
F
o
that pushes the block is at an angle
β
above
the horizontal. Find the force
F
o
.
m
α
β
F
o
1.
m g
1 + sin
α
cos(
β

α
)
2.
m g
1
cos(
α
+
β
)
3.
m g
1

sin
β
cos(
β

α
)
4.
m g
1

sin
β
cos(
α
+
β
)
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homework 08 – BAUTISTA, ALDO – Due: Feb 8 2006, 4:00 am
2
5.
m g
1 + sin
β
cos(
β

α
)
6.
m g
1 + sin
α
cos(
α
+
β
)
correct
7.
m g
1 + sin
β
cos(
α

β
)
8.
m g
1 + sin
β
cos(
α
+
β
)
9.
m g
sin
β
cos(
α
+
β
)
10.
m g
1 + sin
α
cos(
α

β
)
Explanation:
The acceleration up the plane is given,
a
=
g .
The angle that
F
o
makes with respect to
the inclined plane is
α
+
β
. So the component
of
F
o
which is parallel to the inclined plane is
F
o
cos(
α
+
β
)
Therefore
F
o
cos(
α
+
β
)

m g
sin
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 Spring '08
 Turner
 Force, Mass, Work, Car, 9.8 m/s2 . m3 T2 m2

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