Question

20
If external force acting on a system is constant, it means that the
velocity of the CM
1) in constant
2) is variable
3) depends on internal forces
4) all of the above,​

Answer 1

Answer ⤵️

Acceleration of centre of mass

a

cm

=

M

F

ext

If no external force acts on the a system of particles i.e.

F

ext

=0

⟹

a

cm

=0

The acceleration of centre of mass is zero and so it will continue to move with its initial velocity.

Thus Assertion is incorrect.

rate of change of linear momentum of the system

dt

d

P

=

F

ext

∴

dt

d

P

=0 (∵

F

ext

=0)

⟹

P

= constant

Thus if no external force acts on the system, then linear momentum of the system is conserved.

So, Reason is incorrect.