NAEST-2020 Balloon and Wall: The forces on a balloon release

Question: NAEST-2020 Balloon and Wall: The forces on a balloon released in the vicinity of a wall
Air is coming out of the balloon but the balloon is not going backward. This is a violation of

1. Newton's first law
2. Newton's second law
3. Newton's third law
4. None of these

Question 2: For which of the following systems, the linear momentum remain the same while the air is coming out of the balloon?

1. The balloon
2. The air within the balloon
3. The initial air within the balloon
4. The balloon with the air within
5. The balloon with the initial air within
6. None of these

Question 3: The outgoing air in the neck of the balloon exerts a force on

1. the neck of the balloon
2. the part of the balloon in contact with the wall
3. the remaining air of the balloon
4. The air outside

Question 4: Considering that air is coming out of the balloon in the horizontal direction, the force by the balloon on the wall has a positive component

1. In the vertically upward direction
2. In the vertically downward direction
3. In the horizontal direction towards the wall
4. In the horizontal direction away from the wall

Solution 1: Newton's laws are not violated. The force applied by the outgoing air on the balloon is balanced by the reaction force from the wall. The resultant force on the balloon is zero. Hence, it is not going backward.

Solution 2: Look at the centre of mass of the balloon (rubber part). Initially (at the instant of release), it is stationary and its momentum is zero. The centre of mass moves towards the wall as air starts coming out of the balloon. Thus, the balloon has non-zero momentum towards the wall as air comes out of the balloon. Thus, momentum of the balloon is not constant.

Solution 3: The outgoing air in the neck of the balloon exert a force on all objects in its vicinity i.e., (a) the neck of the balloon (c) remaining air of the balloon (d) the air outside.

Solution 4: The outgoing air applies a horizontal force on the balloon towards the wall. Thus, the wall applies a a horizontal force away from the wall.

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