AP Physics C
Name_______________________________
Study Guide Ch 8
http://ecc.pisd.edu
Center of Mass, Linear Momentum, Collisions
I. OBJECTIVES: Upon completion of this unit you should be able to
a. Find the center of mass of a system of particles
b. Relate the impulse acting on a mass to its change in momentum.
c. Apply conservation of momentum to various systems and collisions.
II. APPROXIMATE SCHEDULE:
F
11/1 Crash Test Bumper
M
T
W
Th
F
11/4
11/5
11/6
11/7
10/8
Begin Ch. 8 Center of Mass
Continue Center of Mass
Linear Momentum, Force and Change in Momentum
Conservation of Momentum
Impulse and Momentum,
M
T
W
Th
F
11/11
11/12
11/13
11/14
11/15
Collisions
Collision of Carts Lab
Continue Collisions
Collisions in Two Dimensions
Continue Ch 8
M
T
11/18 Finish Ch. 8
11/19 Test Ch 8
ASSIGNMENTS:
DUE DATES
Crash Test Bumper…………………………………………………….F 10/31
Center of Mass Activity……………………………………………….T 11/5
Collision of Carts Lab ...........................................................................W 11/12
Collision in 2-D Lab…………………………………………………...Th11/14
Ch 8 problems #7, 9, 14, 18, 23, 33, 35, 49, 69, 89, 94, 112.…….......T 11/19
Test Ch 8…............................................................................................T 11/19
AP Physics C
Center of Mass Quiz: True or False?
Name____________________________
____ 1. The center of mass of an object is the point at which all of the mass of the object can be considered
to be concentrated.
_____2. The center of mass of an object is always the center of gravity as well.
_____3. An object can have more than one center of mass.
_____4. The center of mass of an object must physically lie on the object.
_____5. The lower the center of mass of an object, the more stable the object is.
_____6. Ultimately, all forces acting on an object act on its center of mass.
_____7. According to Newton’s first law, the motion of the center of mass of an object is changed only if a
net force acts on the center of mass of the object.
_____8. If there is a net force acting on an object, the center of mass will accelerate.
_____9. If an object is initially at rest, and then explodes, the center of mass of the object’s fragments
remains at rest.
_____10. If a projectile explodes while still in flight, the center of mass of the fragments will continue to
follow a parabolic path.
Center of Mass Activity
Directions: Obtain a block of wood and a ruler or meter stick from your teacher. Draw a diagram of the
block with three edges placed on a coordinate axes as shown below, labeling the lengths and positions of
the holes in the block in centimeters. Assuming that each hole can be considered to be uniform and one
centimeter in diameter, find the coordinates of the center of mass of the block.
Ch. 8 Even-numbered homework problem answers:
14. ycm = 3/5 b
18. vcm = 3 i – 1.5 j
94. (a) vcm = 3 m/s
(b) u3 = 2 m/s ; u1 = - 6 m/s
(c) u3’ = - 2 m/s ; u1’ = 6 m/s
(d) v3’ = 1 m/s ; v1’ = 9 m/s
(e) 42 J
112. (a) vball = vblock = 6.26 m/s
(b) d = 20 m