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Ph 111.01
October 15, 2008
PS 7b (18)
Problem 1.
On a horizontal frictionless table, masses A and B (3 kg,
6
kg) slide to the right and left,
respectively. They have speeds of 3 m/s and 1 m/s, respectively. The two masses collide, and bounce
off each other. After the collision, they travel in opposite directions at speeds of 1.5 m/s and
1.250
m/s,
respectively.
(Note: In this problem, please use + dir = right,  dir = left, to indicate direction.)
a.)
Calculate A's momentum:
before collision:
kg·m/s
after collision:
kg·m/s
Explain why it is NOT conserved.
b.)
Calculate B's momentum:
before collision:
kg·m/s
after collision:
kg·m/s
Explain why it is NOT conserved
c.)
Calculate the A+B system's momentum:
before collision:
kg·m/s
after collision:
kg·m/s
Explain why it IS conserved.
d.)
Calculate the kinetic energy of the A+B system:
before collision:
J
after collision:
J
What kind of collision is this?
m
A
m
B
v
1A
v
1B
before
m
A
m
B
v
2A
v
2B
after
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View Full DocumentSolution.
We are assuming that this is a colinear collision, without bouncing off to the side.
Things are complicated enough that we will just take a completely algebraic approach, where
velocity to the right will have a positive sign, and velocity to the left, a negative sign.
Thus we
have:
1
1
2
2
3 m/s
1 m/s
1.5 m/s
1.25 m/s
A
B
A
B
v
v
v
v
= +
=−
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 Fall '08
 Staff
 Friction, Mass

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