If net force on a system of particles is zero. Then
`{:(,"Column I",,"Column II",),((A),"Acceleration of centre of mass",(p),"Constant",),((B),"Velocity of centre of mass",(q),"Zero",),((C ),"Momentum of centre of mass",(r ),"May be zero",),((D),"Velocity of an individual particle of the system",(s),"May be constant",):}`

Answer

To solve the question, we need to analyze the implications of having a net force of zero on a system of particles. Let's break it down step by step.

### Step 1: Understanding the Implication of Zero Net Force
When the net force acting on a system of particles is zero, according to Newton's second law, we have:
\[ F_{\text{net}} = m \cdot a_{\text{cm}} \]
where \( a_{\text{cm}} \) is the acceleration of the center of mass. If \( F_{\text{net}} = 0 \), then:
\[ a_{\text{cm}} = 0 \]
This means that the acceleration of the center of mass is constant, specifically zero.

**Hint:** Remember that zero net force implies no change in velocity, hence zero acceleration.

### Step 2: Analyzing the Velocity of the Center of Mass
Since the acceleration of the center of mass is zero, it follows that the velocity of the center of mass must be constant. This means that:
- The velocity of the center of mass can be a constant value (which could be non-zero) or it could be zero.

**Hint:** Consider that constant velocity means no acceleration; thus, the center of mass maintains its velocity.

### Step 3: Analyzing the Momentum of the Center of Mass
The momentum of the center of mass \( P_{\text{cm}} \) is given by:
\[ P_{\text{cm}} = m \cdot v_{\text{cm}} \]
Since the velocity of the center of mass is constant, the momentum of the center of mass is also constant. However, if the center of mass is at rest (velocity is zero), then the momentum can also be zero. Thus:
- The momentum of the center of mass is constant and may be zero.

**Hint:** Momentum is directly related to velocity; if velocity is constant, momentum is constant too.

### Step 4: Velocity of Individual Particles
The velocities of individual particles in the system can vary. While the center of mass has a constant velocity, individual particles can have different velocities that may change. Therefore:
- The velocity of an individual particle may be constant or may change, depending on the system.

**Hint:** Individual particle motion can be complex, even if the center of mass moves uniformly.

### Conclusion
Now, we can match the items from Column I with Column II based on our analysis:

- **(A)** Acceleration of center of mass → **(p)** Constant (since \( a_{\text{cm}} = 0 \))
- **(B)** Velocity of center of mass → **(q)** Constant (may be zero)
- **(C)** Momentum of center of mass → **(r)** May be zero (but constant)
- **(D)** Velocity of an individual particle of the system → **(s)** May be constant (depends on the particle)

### Final Matching:
- A → p (Constant)
- B → q (Zero or Constant)
- C → r (May be Zero)
- D → s (May be Constant)