Answer:
A
Step-by-step explanation:
The angular momentum of a system of particles around a point in a fixed inertial reference frame is conserved if there is no net external torque around that point:
d
→
L
d
t
=
0
or
→
L
=
→
l
1
+
→
l
2
+
⋯
+
→
l
N
=
constant
.
Note that the total angular momentum
→
L
is conserved. Any of the individual angular momenta can change as long as their sum remains constant. This law is analogous to linear momentum being conserved when the external force on a system is zero.