Question

According to principle of conservation of energy, the total momentum of a system of masses in any direction remains constant unless acted upon by an external force in that direction.

A.TrueB.False

Answer 1

momentum of system of body is constant when any external force applied on that systems is equation to zero .
because we know ,
change in momentum per unit time is called force
e.g.
dP/dt=Fext
if Fext =0
then ,
dP/dt =0
it means
Pf-Pi = constant

but external force is constant then
dp/dt =K {Fext =constant =K
dp=Kdt
Pf-pi =Kt
we see
change in momentum is variable.
so, we can say that above statement is false because force is constant hence momentum is variable.

Answer 2

The given statement above is true