Rocket works on the principle of conservation of :

Question

Accepted Answer

Rocket propulsion operates on the principle of conservation of momentum, which is why Option 2 is the correct answer.

1. **Explanation for Option 2 (Momentum):**
   - The principle of conservation of momentum states that in a closed system, the total momentum remains constant if no external forces act on it. Rockets work by expelling gas at high speed in one direction, which results in the rocket moving in the opposite direction. This is a direct application of Newton's third law of motion: for every action, there is an equal and opposite reaction. As the rocket expels gas, the momentum of the gas moving backward is equal and opposite to the momentum gained by the rocket moving forward. Thus, the total momentum of the system (rocket plus expelled gas) remains constant, demonstrating the conservation of momentum.

2. **Explanation for why other options are incorrect:**
   - **Option 1 (Force):** While forces are involved in rocket propulsion (thrust is a force), the principle that governs the operation of rockets is not the conservation of force. Forces cause changes in motion, but they are not conserved quantities. The conservation principle relevant to rockets is momentum, not force.
   - **Option 3 (Velocity):** Velocity is a vector quantity that describes the speed and direction of an object. While the velocity of the rocket changes as it accelerates, velocity itself is not conserved. The conservation principle that applies is momentum, which involves both mass and velocity.
   - **Option 4 (Mass):** Mass is not conserved in the context of rocket propulsion because the rocket loses mass as it expels fuel. The conservation principle that applies is momentum, which accounts for the changing mass of the rocket as it burns fuel and expels exhaust gases.

In summary, the correct principle that explains how rockets work is the conservation of momentum, making Option 2 the correct answer.