Question

When one unties the mouth of a balloon, compressed air rushes to the left side with high speed. Then towards which side will the balloon move?

Answer 1

When you untie the mouth of a balloon, compressed air rushes to the left side with high speed. Since initially air was inside the balloon and it was at rest and no external force was acting on it. When you untie the balloon air moves to the left.

Sinc the external force on the balloon is zero, hence we can conserve the momentum of the balloon and air as a system.

If the air moves to the left then balloon will get an impulse in the opposite direction (right side) as momentum of the system is constant.

Hence, balloon will moves towards right direction.