C4_presentation - Suppose a system of particles experiences...

Suppose a system of particles experiences no external
interactions. What else must be true?
(A) It also experiences no internal interactions.
(B) Its total momentum is not conserved.
(C) Its center of mass is stationary.
(D) The system’s total momentum is constant.
(E) None of the above.

Total momentum defined:
N tot
p p p p
   
+ + + = ...
2 1
The Law of Conservation of Momentum: The total
momentum of an isolated system does not change
with time.

x (east)
y (north)
v = 5.0 m/s
v = 2.0 m/s
Two 3.0-kg blocks are sliding
along an icy surface with
velocities as shown in the
diagram at left . What is the
total momentum of the
two blocks?










⋅
=
0
0
m/s kg 0 . 15
1
p











⋅ =
0
m/s kg 6.0 -
0
2
p











⋅
⋅
= + =
0
m/s kg 6.0 -
m/s kg 0 . 15
2 1
p p p
tot
  

(C4T.2) The following diagrams show hypothetical results for
collisions between two identical balls floating in space. The
white ball was initially moving to the right along the dotted line
before it hit the gray ball, which was initially at rest. (The
collision is not necessarily head-on.) The arrows depict the
balls’ final velocities. Which outcomes are physically possible?