010
10.0points
A system of two wheels fixed to each other is
free to rotate about a frictionless axis through
the common center of the wheels and per-
pendicular to the page.
Four forces are ex-
erted tangentially to the rims of the wheels,
as shown below.
2
F
What is the magnitude of the net torque on
the system about the axis?
10.0points
In the absence of air resistance, a ball thrown
vertically upward with a certain initial speed
will return to its original level with the same
speed.
When air resistance is a factor affecting the
ball, compare its speed to its initial speed
when it returns to its original level.
1.
less than its original speed
correct
2.
More information is needed.
3.
the same as its original speed
The three forces
F
apply counter-clockwise
torques while the other force 2
F
applies a
clockwise torque, so
τ
=
summationdisplay
F
i
R
i
011
10.0points
Robin pushes a wheelbarrow by exerting a
147 N force horizontally. Robin moves it 83 m
at a constant speed for 22 s.
What power does Robin develop?
012
10.0points
In the absence of air resistance, a ball thrown
vertically upward with a certain initial speed
will return to its original level with the same
speed.
When air resistance is a factor affecting the
ball, compare its speed to its initial speed
when it returns to its original level.
1.
less than its original speed
correct
2.
More information is needed.
3.
the same as its original speed

Version 050 – Midterm 02 – yao – (92695)
6
4.
more than its original speed
Explanation:
The ball loses mechanical energy due to the
negative work done by the air resistance, so
when it returns to its starting point and to
its original potential energy, it will have less
kinetic energy and therefore less speed.

013
10.0points
Two satellites A and B are orbiting the Earth
in concentric circular orbits.
Satellite B has
twice the mass of satellite A, and the distance
of satellite B from the Earth’s center is twice
that of satellite A.
What is the ratio of the tangential speed of
B to that of A?
v
0
m
m
What value of
v
0
would be required in terms
of
g
and
ℓ
?
014
10.0points

Version 050 – Midterm 02 – yao – (92695)
7
E
i
=
E
f
KE
i
+
PE
i
=
KE
f
+
PE
f
1
2
(2
m
)
v
2
+ 0 = 0 + (2
m
)
g ℓ
1
2
parenleftbigg
1
2
v
0
parenrightbigg
2
=
g ℓ
v
0
=
radicalbig
8
g ℓ
= 2
radicalbig
2
g ℓ .
015
10.0points