Question

Net external force acting on a system of particles is zero and the internal forces obey the law of action and reaction. Which of the following is not correct?
Options:
a)Position of centre of mass of system may change
b)Velocity of centre of mass of system cannot change
c)Linear momentum of system cannot change
d(Kinetic energy of system cannot change​

Answer 1

Answer:

a) position of centre of mass of system may change

Answer 2

Answer:

a) Position of center of mass of system may change.

Step-by-step explanation:

When a net external force acting on a system of  particles is zero and the internal forces obey the law of action and reaction.

We know that when net external force acting on system of particles is zero then acceleration of center of mass system will be zero.

When the acceleration of the center of mass of system is zero then the velocity of the center of mass of the system  will be constant.

When the velocity of center of mass of system constant it means the position of center of mass has to be change because

$Velocity=\frac{dx}{dt}$

Position of center of mass is given by

$Mr=\sum_{i=0}^{n}m_ir_i$

Differentiate w.r.t t then, we get

$M\frac{dr}{dt}=\sum_{i=0}^{n}m_i\frac{dr_i}{dt}$

$MV=\sum_{i=0}^{n}m_iv_{i}$

Therefore , the position of center of mass should be change.

Therefore, the correct option is a.

Answer: a) Position of center of mass of system may change.