PHYS 2101

1
PHYS 2101
Fall 2009

• Angular Momentum and Torque
• II. Conservation of Angular Momentum

2
PHYS 2101
Fall 2009
EX1
A 5-kg object is located at
meters in a particular coordinate system. It
is moving with a velocity of
m/s. What is the angular momentum of the
object about the origin?
3
PHYS 2101
Fall 2009
EX2
A penguin of mass m falls from rest from the edge
of a crevice in the ice. What is the angular
momentum of the penguin about a point 10 meters
away on the other side of the crevice?
10 m
4
PHYS 2101
Fall 2009
EX2
A penguin of mass m falls from rest from the edge
of a crevice in the ice. What is the angular
momentum of the penguin about a point 10 meters
away on the other side of the crevice?
5
PHYS 2101
Fall 2009
A penguin of mass m falls from rest from the edge
of a crevice in the ice. What is the torque on
the penguin about a point 10 meters away on the
other side of the crevice due to the
gravitational force?
EX3
10 m
6
PHYS 2101
Fall 2009
A penguin of mass m falls from rest from the edge
of a crevice in the ice. What is the torque on
the penguin about a point 10 meters away on the
other side of the crevice due to the
gravitational force?
EX3
7
PHYS 2101
Fall 2009
CT1
About which point shown below will the penguin
have the largest angular momentum as it falls?
1 - A 2 - B 3 - C 4 - D 5 - E 6 - F
A
B
F
C
D
E
8
PHYS 2101
Fall 2009
EX4
A 5-kg object is located 5 meters due north of
the origin. It is moving at a speed of 20 m/s at
an angle of 30 above the horizontal. What is
the angular momentum of the object about the
origin?
9
PHYS 2101
Fall 2009
EX5
A 35-g wad of putty falls onto one end of a
horizontal uniform rod that is pivots about its
center of mass and sticks. If the wad is
traveling at 8 m/s when it hits and rod is 70 cm
and has a mass of 3.5 kg, how what is the angular
speed of the rod and putty after the collision?
10
PHYS 2101
Fall 2009
EX6
A disk, of mass 440 g and radius 3.5 cm, is
rotating at 18.9 rad/s on a frictionless shaft of
negligible radius. Another disk, of mass 270 g
and radius 2.3 cm, is initially not rotating and
dropped down the shaft onto the first disk.
Frictional forces act to bring the two disks to a
common rotational speed. Find the final
rotational speed of both disks.
11
PHYS 2101
Fall 2009
CT2
Which of the following is true about the energy
of the two disks? 1 - Ei gt Ef 2 - Ei Ef 3 -
Ei lt Ef
12
PHYS 2101
Fall 2009
EX7
A 0.5-m long uniform rod of 2 kg rotates about a
pivot through one end of the rod. It is held
horizontally and then released. When it is
vertical, it collides with a 0.2 kg wad of putty
that sticks to the rod. What is the angular
speed of the rod just after the collision?