Question

In which situation does the law of conservation of momentum apply?

Answer 1

As per Newton's II law we know that

$F = \frac{dP}{dt}$

rate of change in momentum is Net outside force on the object

now here we will have if net outside force will be zero

then we can say

$F = 0 = \frac{dP}{dt}$

so from above equation we can say

$dP = 0$

and hence we have

$P = constant$

so the correct answer will be

3.) in the absence of outside forces