Question

Recoil of a gun is an example of which principle?

• A. Conservation of mass
• B. Conservation of energy
• C. Conversion into kinetic energy
• D. Conservation of linear momentum

Hint:

Think about total momentum of the gun and bullet system before and after firing.

Answer 1

The Correct Option is D

Step 1: Before the gun is fired, both the gun and the bullet are at rest. Total momentum of the system is zero.

Step 2: When the trigger is pulled, hot gases push the bullet forward with high speed. By Newton's third law, the gases push back on the gun with an equal and opposite force.

Step 3: Since there is no outside horizontal force on the gun bullet system, momentum is conserved. So the forward momentum gained by the bullet must be balanced by an equal backward momentum gained by the gun. In symbols, \(m_{bullet} v_{bullet} + m_{gun} v_{gun} = 0\).

Step 4: This backward motion of the gun is what we call recoil. Because the gun has a much larger mass than the bullet, its recoil velocity is much smaller than the bullet's forward velocity, even though both have equal and opposite momentum.

Step 5: The other options are wrong. No mass is destroyed or created, so mass conservation is not the special idea being tested. Energy is also conserved here but the recoil effect itself is explained by momentum, not by energy alone. Conversion into kinetic energy is just a side effect, not the underlying law. So the correct answer is conservation of linear momentum.