Unit 7 WS 5
Name:____________________________________________
Part 1 – Center of mass of a system
1A
B
C
The objects below have equal mass. Think of these two objects as one system. Draw a dot where you
think the center of mass of this system is.
In the grid below, each box represents 1 meter. Object B is at rest. Object A is moving to the right at
3 m/s. The picture below shows each object’s position at t = 0 seconds. Draw a dot showing the
location of the center of mass of the system at each second for the next 3 seconds.
Based on the dots you drew, what is the velocity of this system’s center of mass?
1m
A
2A
B
C
B
Think of the two objects below as one system. The objects have equal mass. Draw a dot where you
think the center of mass of this system is.
In the grid below, each box represents 1 meter. Object A is moving right at 2 m/s. Object B is
moving left at 1 m/s. The picture below shows each object’s position at t = 0 seconds. Draw a dot
showing the location of the center of mass of the system at each second for the next 3 seconds.
What is the velocity of the center of mass of this system?
1m
A
3A
B
C
B
B
C
Velocity
of CM =
m
____
s
Think of the two objects below as one system. Object A is twice the mass of object B. Draw a dot
where you think the center of mass of this system is.
Object A is moving right at 2 m/s. Object B is moving left at 1 m/s. The picture below shows each
object’s position at t = 0 seconds. Draw a dot showing the location of the center of mass of the system
at each second for the next 3 seconds.
What is the velocity of the center of mass of this system?
B
A
4A
Velocity
of CM =
m
____
s
Velocity
of CM =
m
____
s
Think of the two objects below as one system. Object A is twice the mass of object B. Draw a dot
where you think the center of mass of this system is.
Object A is moving left at 2 m/s. Object B is moving right at 1 m/s. The picture below shows each
object’s position at t = 0 seconds. Draw a dot showing the location of the center of mass of the system
at each second for the next 3 seconds.
What is the velocity of the center of mass of this system?
A
B
Velocity
of CM =
m
____
s
Conservation of Momentum
5.) Granny whizzes around the ice rink and sees her grandson Ambrose who is at rest directly in her path. Rather than knock
him over, she picks him up and continues in motion without braking. Consider both Granny and Ambrose as two parts of one
system.
a. Complete the following table (in what ever order
makes sense to you!!)
Granny
Ambrose
Mass
vbefore
vafter
∆v
pbefore
pafter
∆p
Impulse
System
(think of the center of mass)
(add the two individual momentums)
b.
How does the impulse experienced by Granny compare to the impulse experienced by Ambrose?
c.
How does Granny’s change in momentum compare to Ambrose’s change in momentum?
d.
Use your answer to part (c) to determine the change in momentum of the system.
e.
How does the total momentum of the system before the collision compare to the total momentum after the collision?