Q18CQ - College Physics (Urone)

Question

Why does an ordinary rifle recoil (kick backward) when fired? The barrel of a recoilless rifle is open at both ends. Describe how Newton’s third law applies when one is fired. Can you safely stand close behind one when it is fired?

Step-by-Step Solution

Answer

The rifle shoots a bullet with a huge amount of force, and hence the bullet applies a backward force on the rifle according to Newton’s third law of motion. 

Yes, one can stand behind the rifle when fired when it is put close to the shoulder.

Step 1: Concept of Newton’s third law of motion

Newton’s Third Law of Motion states that whenever a body exerts a force on another body, the first body experiences a force that is equal in magnitude and opposite in direction to the force that it exerts.

Step 2: Reason for rifle recoil when fired

The rifle shoots a bullet with a huge amount of force, and hence the bullet applies a backward force on the rifle according to Newton’s third law of motion. 

In the above case, the force exerted by the rifle on the bullet is given back by the bullet, which is equal in magnitude but opposite in direction.

Step 3: Describe the application of Newton’s third law on the recoilless rifle

When the rifle is open at both ends, the air is pushed backward rather than the rifle itself.

Step 4: How to make it safe to stand behind a rifle when fired

Standing behind the rifle when fired is safe when it is put close to the shoulder. In this way, the whole body absorbs the sudden force.