Q9.1.a
Two pucks lie on ice and can slide with little friction. A string is attached to each puck and the string is pulled with a constant force F. The
string is wound around the outer edge of puck 1 but attached to the center of puck 2. They both start from rest. Try to imagine what you
would see as they move. What do you think will happen in the next 3 seconds?
2
1) 1 will move farther than 2
2) 2 will move farther than 1
3) 1 and 2 will move the same distance
F
Just to see what they think. No correct answer.
F
1
Q9.1.b
Two pucks lie on ice and can slide with little friction. A string is attached to each puck and the string is pulled with a constant force F. The
string is wound around the outer edge of puck 1 but attached to the center of puck 2. They both start from rest. Apply the momentum
principle to each puck. What does it predict should happen in the next 3 seconds?
2
1) 1 will move farther than 2
2) 2 will move farther than 1
3) 1 and 2 will move the same distance
1
The VPython program referred to in the following questions (9.1a - 9.2a) is
09_Krel.py
Q9.1.a : Watch the objects move (VPython program)
Which object has the greater total momentum (magnitude)?
1) Top object (blue)
2) Bottom object (red)
3) Their total momentum is the same
Q9.1.b : Watch the objects move (VPython program)
Which object has the greater total kinetic energy?
1) Top object (blue)
2) Bottom object (red)
3) Their total kinetic energy
is the same
Q9.2.a : Watch the objects move (VPython program)
Which object has the greater translational kinetic energy
(KTRANS)?
1) Top object (blue)
2) Bottom object (red)
3) Their translational kinetic energy
is the same
F
F
The VPython program referred to in the following questions is
09_RotateVibrateTranslate.py
Q9.2.b : Watch the object move (VPython program) CASE = 0
Ball on right (red) moving in +x direction, spring stretching, ball
on left (blue) at rest.
1) +x
2) –x
3) 0 (no direction)
What is the direction of 𝑣⃗𝐶𝑀 ?
Q9.2.c: Watch the object move (VPython program) CASE = 0
Ball on right (red) moving in +x direction, spring stretching, ball
on left (blue) at rest.
1) +x
2) –x
3) 0 (no direction)
What is the direction of 𝑣⃗𝑅𝐸𝐿 for the left ball (blue)?
Q9.2.d, 9.2.e, 9.2.f: Watch the object move (VPython program) CASES = 1 - 6
In the case shown in the VPython program, what energy
1) Ktrans
terms are nonzero for the system of the two balls and
2) (Kvib + Uspring) 1
the spring?
3) Krot
4) (Kvib + Uspring) and Krot
5) Ktrans and Krot 2
6) Ktrans and (Kvib + Uspring) 4, 6
7) (Kvib + Uspring) and Krot and Ktrans 3, 5
Q9.2.g, 9.2.h: Watch the object move (VPython program) CASE = 4
The system starts from rest. A constant force is applied
1) Ktrans
to the right (red) ball, so
2) (Kvib + Uspring)
Wext > 0.
3) Krot
4) Ktrans + Krot
What energy terms increase?
5) Ktrans and (Kvib + Uspring)
6) (Kvib + Uspring) and Krot
7) (Kvib + Uspring) and Krot and Ktrans
Q9.3.a: A diatomic molecule such as molecular nitrogen (N2) consists of two atoms each of mass M, whose nuclei are a distance d apart.
What is the moment of inertia of the molecule about its center of mass? (See example on page 355)
1) Md 2
2) 2Md 2
3) 1
Md 2
2
4) 1
Md 2
4
5) 4Md 2
d
Q9.3.b: The spokes of a bicycle wheel have low mass, so almost all of the mass of the wheel is concentrated in the rim. What is the
moment of inertia of a bicycle wheel of radius R and mass M? (See example on page 355)
1) MR2
2) 2  MR2
3) 2  RM
4) (1/2) MR2
5)  MR2
Q9.3.a
Two balls of mass 0.7 kg are connected by a low mass rigid rod of length 0.4 m.
The object rotates around a pivot at its center, with angular speed 13 radians/s.
What is the rotational kinetic energy of this object?
1) 484 J
2) 4.73 J
3) 2.37 J
4) 0.056 J
5) 0 J
I = 2MR 2 = 2(0.7)(0.2)2 = 0.056 kg × m 2
KErot = 12 Iw = (0.5)(0.056)(13 )
2
2
Q9.4.a Through what distance did the force act on the Point Particle system?
1) 0.03 m
2) 0.04 m
3) 0.07 m
4) 0.08 m 5) 0.10 m
Q9.4.b Through what distance did the force act on the Real system?
1) 0.03 m
2) 0.04 m
3) 0.07 m
4) 0.08 m 5) 0.10 m
Q9.4.c Which is the energy equation for the Point Particle system?
1) Ktrans = F*(0.07 m)
2) Ktrans = F*(0.08 m)
3) Ktrans + Kvib + Uspring = F*(0.07 m)
4) Ktrans + Kvib + Uspring = F*(0.08 m)
Q9.4.d
For the Point Particle system, what
was the total external work?
You pull up with constant force F
1) F*b + –mg*b
2) F*a + –mg*b
3) F*(a+b) + –mg*(b)
4) F*(a+b) + –mg*(a+b)
Q9.4.e
For the Real system, what
was the total external work?
1) F*b + –mg*b
2) F*a + –mg*b
3) F*(a+b) + –mg*(b)
4) F*(a+b) + –mg*(a+b)
You pull up with constant force F
Q 9.4.f: A skater pushes straight away from a wall. She pushes on the wall with a force whose magnitude is F, so the wall
pushes on her with a force F (in the direction of her motion). As she moves away from the wall, her center of mass moves a
distance d. What is the correct form of the energy principle for the real system consisting of the skater?
1) K  E
 Fd
trans
internal
2) K
trans  Einternal   Fd
3) K
 E
0
4)
trans
internal
K trans  Fd
5) K
trans   Fd
Q9.4.g: A skater pushes straight away from a wall. She pushes on the wall with a force whose magnitude is F, so the wall pushes on her
with a force F (in the direction of her motion). As she moves away from the wall, her center of mass moves a distance d. What is the correct
form of the energy principle for the point particle system for the skater?
1) K
 E
 Fd
2)
3)
4)
trans
internal
K trans  Einternal   Fd
K trans  Einternal  0
K trans  Fd
5) K
trans   Fd
Q9.4f
You pull on both ends of a spring. Each hand exerts a constant force of 5
N. Each hand moves a distance of 0.4 meters, so the spring is stretched
a total of 0.8 meters.
Consider the spring as a real system.
What is the change in the total energy of the spring due to the
work done by you?
1) 0 J
2) 2 J
3) 4 J
4) 5 J
Q9.4g
You pull on both ends of a spring. Each hand exerts a constant force of 5 Consider the spring as a point particle. Calculate the change in
N. Each hand moves a distance of 0.4 meters, so the spring is stretched the translational kinetic energy of the spring.
a total of 0.8 meters.
Ktrans =
1) 0 J
2) 2 J
3) 4 J
4) 5 J
Q9.4h
You pull on both ends of a spring. Each hand exerts a constant force of 5
N. Each hand moves a distance of 0.4 meters, so the spring is stretched
a total of 0.8 meters.
You did 4 J of work on the spring, but the translational kinetic
energy of the spring did not change. What happened to the 4 J
of energy you expended?
1) The spring potential energy increased
2) The spring potential energy decreased
3) The 4 J was lost